Do-it-yourself skimmer for your cephalopod tank

By: Lawfish - June 8, 2003

I would like to make several comments before I begin this article. First, I do not intend to represent that I invented this type of skimmer. I based the design upon a Skimmer which was built by a member of Reef Central. Second, the current incarnation of this skimmer is for in-sump (or next to sump) use. The water outlet must be allowed to flow without being plumbed above the top of the mixing box or it will fill the riser with water instead of foam.

I strongly suggest that you read the entire article before you begin building (or even buying supplies). There are a couple of variations depending on the size pump that you choose to use. Also, determine where you intend to install the skimmer (in or next to sump) and take measurements to insure that it (and any necessary plumbing) will fit in that space. Finally, because this skimmer is built from acrylic, I will include a section on the basics of working with acrylic. If you get stuck or do not understand something feel free to send me a PM and I will try to help in any way that I can.

Table of Contents

I. Acrylic Basics
a. Cutting acrylic sheet and tube
b. Preparing edges for joining
c. Drilling acrylic
d. Joining acrylic
e. Finishing acrylic
f. Sources for acrylic sheet, tube and supplies

II. Do It Yourself Skimmer
a. Necessary Materials
b. Cutting and preparing pieces of the mixing box
c. Cutting the acrylic tube
d. Preparing flanges and gaskets
e. Preparing first riser tube and water inlet chamber
f. Preparing collection cup and second riser tube
g. Assembly of mixing box
h. Installing internal plumbing and baffle
i. Attaching riser and inlet chamber to the top panel
j. Water inlet nozzle
k. Completing assembly of mixing box
l. Installing waste drain on collection cup
m. Final assembly
n. Water pump choice
o. Set up

I. Acrylic Basics
Cutting acrylic

This section will discuss the tools which are necessary to work with acrylic. Some you cannot do without and others are either optional or less expensive substitutes are readily available. I will endeavor to provide at least one source for each example as I go along.


One of the most important aspects of working with acrylic is to get straight and relatively "clean" cuts. If you are not able to do so it will be difficult, if not impossible, to achieve seams which are solid, and more importantly, water-tight.

There are several tools which can be used to cut acrylic, the most popular of which is the good old circular saw. Either a handheld circular saw or a table saw can be used to cut acrylic. The table saw is by far the better choice if you have access to one. It allows you to get a nice straight cut without too much trouble (or bloodshed - just kidding - however, let me remind you to please use eye and ear protection whenever using power tools. This is particularly true when working with acrylic because a flying piece of acrylic can be very sharp). If you are going to use a circular saw you will have to have a means of making a straight cut. This can be easily accomplished by using a 2 x 4 (or some other straight edge like a level) as a guide. If you clamp the guide on top of the acrylic, you can then run the saw along the straight edge to make your cut.

Whether you use a circular saw or a table saw, you should not try to use a plain old cross cut blade. If you do the edges will likely be chipped resulting in difficulty in joining and weak seams. Make sure to use a carbide tipped blade. Non-carbide tipped blades very quickly become dull and useless. Finding an appropriate blade for acrylic can be complicated and expensive. There are saw blades made specifically for cutting acrylic. As you may have noticed, they are VERY expensive. However, you can get by with other saw blades. Try to find a saw blade with "Triple Chip Cut". A safe bet is to look for a blade made for cutting laminates like melamine. I purchased a 10" blade, for my table saw, made for cutting laminates at Lowe's for $45.00. If you can't find a laminate blade, try to get a blade with 60 - 80 teeth. Remember to always check eBay - you'd be surprised at what you can find there - or go to your local home supply store and ask for a blade for cutting laminates and plastics and you should be fine.

You can also use a jig saw to cut acrylic. Again, make sure to use a straight edge to guide the saw (I have found that this can be difficult with a jig saw). Use a blade with approximately 10 teeth per inch. If you use a blade with more teeth per inch the acrylic will melt as you cut it.

Lastly, If you have access to a band saw it could also be used to cut acrylic. I've never tried to do this so I don't have much information on appropriate blades. I would assume that blades for cutting laminates are available.

Whichever type of saw you use, the most important thing to remember is to take your time. Try to make some practice cuts on scrap material. Most importantly, let the blade do the work - do not cut too quickly as this will result in melting and/or chipping. Try to set the blade height (or depth on a circular saw) to only about a ¼ to 1/8" inch past the acrylic. This will help to cut down on chipping of the edges.

Routers, jointers and scrapers

The next most important aspect of working with acrylic is getting clean edges so that you can get strong seams. As mentioned above, a good saw blade will result in a clean cut. You can then use a scraper to clean off any small imperfections (Fig. 1). However, you do not have to buy a scraper. Instead, you can use the flat edge of a pair of steel scissors or a flat piece of steel. Just secure the piece of acrylic in a vise or clamp and run the scraper along the edge. Angle the top of the scraper slightly towards you so that it doesn't bump and cause pits (Fig. 2). Note: always use two hands when scraping an edge. I only used one because I needed one to take the picture. Ah to be an Octopus!!

If you don't get perfect edges with your saw do not despair. The edges can be finished with several different types of tools other than a scraper. Routers can be used to finish edges for joining. If you are finishing edges with a router use a double fluted bit and a guide to make sure that your edge remains straight. (Single fluted bits are better for circle cutting which I will discuss below). Make sure to take the extra acrylic that will be removed into account when making your initial cut. A jointer is another option for finishing edges. Again make sure to take the acrylic that will be removed into account when making your original cuts. Also be consistent with the way that you use both the jointer and router. For instance, make one pass over each edge, that way you will not end up with incompatible size pieces.

Cutting holes/circles

One important thing which you must be able to do in order to complete this project is to cut holes in and circles from acrylic. You will need to do this in order to make the flanges and the openings in the top of the skimmer. There are several ways to cut holes in acrylic. First, for smaller holes, you can use a hole saw or a sharp spade bit. Normal bimetal hole saws can be used to cut holes in acrylic. You can use either a drill press or a cordless drill. Do not put too much pressure on the drill - take your time. Hole saws and spade bits are really only good for cutting holes up to about 1 ¾" in diameter. (i.e. a cutout for a bulkhead fitting). If you try to use a hole saw for cutting much larger than that you will likely have problems (not to mention that large hole saws are very expensive).

A better choice for cutting flanges (basically a large acrylic circle) is to use either a hole cutting attachment with a drill or a circle cutting attachment on a Roto-zipper or router. My preference is to use a circle cutting attachment on the drill (Fig. 3). They are inexpensive and do a pretty good job. I got one on eBay for around $5.

When using a circle cutter you should reverse the blade depending upon whether you are cutting a hole or a flange (circle). For a flange, turn the sharp pointed edge outwards so that the edge of the flange is as smooth as possible. For a hole, turn the sharp edge inwards so that the inside of the hole is a smooth as possible. This is not mandatory it just makes the finished project look nicer (Fig. 4). It is easier if you cut about half way through the acrylic and then flip it over and cut the rest from the other side.

If you have a Roto-Zip circle cutting attachments for them are available. They cost approximately $20 at any home improvement store. eBay carries them as well. They are not that difficult to use but tend to not leave nice clean edges. However, you will not be joining on those edges and you can sand them smooth if you don't like the look. Many manufacturers make a very similar attachment for plunge routers (with a single fluted bit) and even for Dremel tools.

Cutting acrylic circles/holes

Probably the most difficult thing that you will have to do for this project is to cut acrylic tube to the proper length. You must make sure that the cut is straight all the way through the tube because it will be joined (glued) to the flanges. I cut tube on the table saw in a jig that I made for that purpose (Fig. 5). Note that while I made this jig from acrylic you could just as easily make one from wood.

Set the blade height at ¼" to 1/8" above one side of the tube (i.e. if the tube is ¼" thick I set the blade at ½" high) I then move the tube until it is cut by the blade and just rotate (roll) the tube letting it be cut all the way around. You can also use a jig saw or a circular saw and you can probably set up a jig similar to mine but made in reverse since the blade will be above the acrylic instead of below it.

Drilling acrylic

Drilling acrylic is not difficult and can be done on a drill press or with a cordless drill. There are bits made specifically for cutting acrylic which are inexpensive and I recommend using those. (US Plastic sells them. For this project you will need a ¼" bit and a 5/16" bit.)

Joining acrylic

There are two main ways to join acrylic, capillary cement and viscous cement. They can both be purchased at (Fig. 6). The first thing to do is to make sure that your pieces fit together as snugly as possible (the cleaner your edges are the easier they are to join). For this project you can set up a jig to hold the pieces or you can clamp them in place for joining. If you do not have any clamps you may be able to get away with using only masking tape to hold the pieces in place. (I suggest having at least one clamp. You will need it to hold pieces down when you drill them.)

Capillary cement is the consistency of water and is best for joining edges that fit perfectly without gaps. It will not do a good job if the edges don't fit together perfectly. When using capillary cement you need a dispensing bottle which has a needle on the end. This too, can be purchased at US Plastic (they call it a "plasticator"). Viscous cement is the consistency of syrup and will fill small gaps in the seam without to much of a problem. I use a little plastic squeeze bottle and cut a small hole in the top to apply this type of cement (Fig. 6). I will detail the proper way to join the pieces in the assembly section below. You should get some extra pieces of acrylic so that you can practice.

Sources for acrylic

The first thing that you should do is to see if there is a local plastic dealer or shop that can provide acrylic sheet and tube. It will likely be less expensive and the shop may even cut the pieces for you for a small fee. sells acrylic sheet in smaller sizes. Before ordering the cut sheets check with US Plastic to see if they have any scrap for sale. They often sell cut sheets in all sizes for hobby use by the pound (it is US Plastic part # 86116). They will give you a mix of 1/16, 1/8 and ¼ inch sheets. I've found that if you buy 20 lbs (its only $1.25 per pound) you get enough of an assortment to complete this skimmer and can use the thinner pieces for practice.

II. Do It Yourself Skimmer
Necessary Supplies and some sources

You will need enough ¼" or 3/16" thick acrylic sheet (for this project 3/16" is more than adequate but you can use ¼" if it is more available) to cut the following pieces:

  • 1 piece 4 ½" X 8"
  • 2 pieces 5" X 8"
  • 2 pieces 8" X 8"
  • 1 piece 5" X 8 ½"
  • 1 piece 4 ½" X 7"
  • 2 ea 6" diameter circle
  • 2 ea 4" diameter circle

    You will also need the following:

  • 10 ea 1" nylon screw ¼-20 (US Plastic part# 91448)
  • 10 ea nylon wing nut for above (US Plastic part# 91576) (I'd get a few extra screws and wing nuts they are very cheap.)
  • 1 foot of acrylic tube 2" outside diameter
  • 1 foot of acrylic tube 3.5" outside diameter (Acrylic tube can be purchased here (AES is the only place that I've found that will sell the tube in 1 foot lengths))
  • 1 ea. 1" bulkhead fitting (slip fitting) (you will need two if you intend to plumb the skimmer through the wall of an acrylic sump)
  • 1 ea. 1" PVC 90° elbow
  • 1 ea. PVC Cement
  • 1 ea. PVC Primer
  • 1 foot of ¾" CPVC pipe
  • 1 ea ¾" CPVC to ¾" PVC fitting
  • 1 ea ¾" to ½" PVC bushing
  • 1 ea PVC ½" slip to ½" female thread fitting
  • 1 ea ½" 90 PVC (slip to slip)
    (If you can get a PVC ½" slip to ½" female thread 90 (you can use that instead of the previous two items)
  • 1 foot of 1" PVC pipe (you can get PVC and CPV supplies at any Home Depot or Lowe's)
  • 1 ea ½" male thread 90 elbow to ½" tubing insert
  • 1 ea ½" tubing insert to ½" male thread fitting (if you are using a larger pump ½" male thread to ¾" tube insert. You can getfittings at -- you can also probably get them at your local home shop)
  • 1 ea 1" gate valve (slip fitting) (You can get these at Lowe's or Home Depot)
  • 1 pt acrylic solvent cement (capillary)
  • 1 tube acrylic solvent cement (viscous - Weldon 16)
  • 1 ea applicator for capillary cement (USplastic, again get a couple extra they are cheap)
  • 1 ea plastic squeeze bottle for viscous cement (You can probably get this at your local pharmacy - if not Us plastic has them)
  • 1 piece rubber sheet for gasket (It should be between 1/4" and 1/8" thick and be soft enough so that it will compress and form a good watertight seal. Your local home store may have rubber sheet gasket. If not you can probably use PVC shower liner or try an auto parts store.)
  • 1 tube Marine Goop (You can buy Marine Goop at any home supply store)
Here is a diagram of what the skimmer will look like with all of the measurements
(Diagram 1).

Cutting and preparing pieces of mixing box

The first thing that you need to do is to cut out the necessary pieces (as noted above) for the mixing box. Please remember to wear safety glasses and ear protection. Here is a diagram to help understand which piece goes where (Diagram 2). Don't worry about the holes just yet we will get to those in a moment. Before you begin to cut, make sure that you leave the protective wrap on the acrylic because it will reduce chipping and scratches. I find it helpful to mark the pieces once I have cut them so that I know what is what (Fig. 7).

Ok, now you have to prepare the edges for joining. If you have pretty smooth cuts just use a scraper. If the cuts are rough and/or uneven try to use a router or jointer. Do not sand the edges! If you do it will round them and make it very difficult to get a good joint when you glue them. (note: you are not really gluing the pieces. The cement that you will use is a solvent. It actually melts the edges and they then join together.)

Now you have to drill a hole in the top left corner of the front panel for the bulkhead fitting. The hole has to be 1 ¾" and I suggest using a bimetal hole saw for this job. Hold the bulkhead over the front panel to see where the hole should be so that the bulkhead doesn't stick out past the edge or top of the panel when installed. Make sure to clamp the piece of acrylic down or it will go flying. Now drill your hole slowly don't try to force the drill or it will just melt the acrylic (Fig. 8, Fig. 9, Fig. 10).

Now you have to cut the two holes in the top panel. Unfortunately, they are too big to use a hole saw to cut. You must either use a circle cutter on your drill or a circle cutting attachment on a Roto-Zip or Dremel. Using these types of tools means that you do not have an exact measurement like you do with a drill or hole saw - the measuring marks tend to not be completely accurate. The larger hole should be the same size as the Inside Diameter of the 3 ½" acrylic tube (that is because the tube will sit on top of it and if the hole is any bigger it will fall through, thus, it would be better if the hole was too small rather than too big). The smaller hole should be the same size as the Inside Diameter of the 2" acrylic tube. See Fig. 11 for the placement of the holes. Do not place the holes to close together (within two inches) or the flange on the water inlet tube will be obstructed by the first riser.

The way that I approach this problem is to set the size of my circle cutter to the inside diameter of the tube and then make a practice hole on a piece of 1/8" acrylic. I then sit the tube on the hole and see if it is supported properly. I then make any necessary adjustments and repeat until the practice hole is perfect. Only then do I cut into the top panel. Use an acrylic drill bit to drill a pilot hole as the bit that comes with the circle cutter will not drill acrylic. Take your time, it takes some practice to get things exactly right. (Note: Make sure to securely clamp the piece down before cutting holes or it will move and either shatter or fly off and hurt someone.) Once you have cut the two holes you can put the pieces of the mixing box aside for the moment. Cutting the acrylic tube

As I mentioned above cutting the acrylic tube may be the hardest part of this project. You need to cut four pieces as follows.

[*]1 piece of 2" diameter 4" in length
[*]1 piece of 2" diameter 3" in length
[*]1 piece of 3 ½" diameter 6" in length
[*]1 piece of 3 ½" diameter 4 ½" in length

Note: If you have the capability to cut a 7" diameter acrylic circle you may want to use 4 ½" acrylic tube for this piece as it will make your collection cup bigger. See below in Flanges section.

If you are using a table saw this part should be pretty easy. If you are using a circular or jig saw take your time. Try to make a jig to hold the tube so that your cut will be straight around. It will be joined to the top panel later and if the edge is not relatively straight you will have trouble. Also, only set the blade depth at between ¼" and 1/8" past the wall thickness of the tube. If you try to cut too deeply into acrylic tube it will shatter. After they are cut put aside the 4 pieces of acrylic tube for now

Preparing flanges and gaskets

A flange is nothing more than an acrylic circle. The circle cutter that I have will only cut a circle up to 6" in diameter which is why I have used that measurement. If you can cut a 7" diameter circle, you may want to do that instead. You can the make your collection cup from 4 ½" acrylic tube (as noted above) giving it more capacity.

You have already mastered the art of cutting holes and cutting a circle is the same procedure so this part should be easy. If you are using a circle cutter, turn the cutting blades around so that the flat edge is facing inward. This will make the edge of your circle look nicer. Cut two circles 6" in diameter and two circles 4" in diameter.

Take one of the 6" circles and using the original guide hole cut a hole the same size as the inside diameter of the 3 ½" acrylic tube (Fig. 12). You will end up with a piece that looks like an "O" (Fig. 13). Now take the other 6" circle and cut a hole in the middle the same size as the inside diameter of the 2" acrylic tube.

Now you have to cut the gaskets. Put the 6" flange with the larger hole over the rubber and cut around the outside and the inside circumference. You should end up with a rubber "O" that is the same size as the flange with the larger hole. Next put that flange down and then lay the rubber gasket and the flange with the smaller hole on top of it. Clamp them down together and drill 6 holes around the flange (I try to center them in the flange). Use the 5/16" acrylic drill bit and drill right through both pieces of acrylic and the rubber (Fig. 14).

You now have two flanges and a gasket which can be screwed tight with the acrylic screws. Note: Unless your holes are perfectly spaced the holes will only line up correctly in one position. Its not a bad idea to mark the side of the flanges and gasket with a pencil or sharpie so that you can remember how they line up. Also mark the top and bottom of the flanges for later.

Take the two 4" acrylic circles and cut a hole in the middle of one equal in size to the inside diameter of the 2" acrylic tube. In the center of the other cut a hole 1" in diameter (you can use a hole saw or spade bit for this hole). Repeat the process for making the rubber gasket described above. Now drill four holes around the outside of these gaskets. You will end up with another set of flanges and a rubber gasket (Fig. 15).

Preparing First Riser Tube and water inlet chamber

Take the 6" flange with the larger hole and the 6" length of 3 ½" acrylic tube. The tube gets glued directly to the flange. Run a bead of the viscous cement around the edge of the acrylic tube and then set it on top of the flange. Then put something heavy on top to compress it while it hardens (I use a cast iron weight). Put another bead of viscous cement around the base of the tube where it joins with the flange. Now repeat this process with the 4" flange with the bigger hole and the 4" length of 2" acrylic tube (Fig. 16). Let these pieces set for several hours. Keep in mind that both of these pieces are actually upside down in Fig 16. The flanges will be on top when the skimmer is assembled (Fig. 17). DO NOT Attach risers to top panel yet this is just to show the orientation of these parts.

Preparing collection cup and second riser tube

Take the other 6" flange (with the smaller hole) and the 3" length of 2" acrylic tube. Join the tube to the hole just like you did above. After allowing the joint to set take the 4 ½" length of 3 ½" acrylic tube and glue it onto the flange outside of the smaller tube - try to center it between the screw holes (Fig. 18). This is your collection cup. Note: If you are using larger flanges you can use 4 ½" acrylic tube for the outside of the collection cup.

Assembly of the mixing box

If you marked your pieces earlier you should have no problem remembering which piece goes where. At this point you will only be assembling the base and sides of the box so put the internal baffle and top aside. Put scotch tape under the base sticky side facing up leaving several inches sticking out (Fig. 19). Now place the front (with the bulkhead hole) and back panels in place and wrap the tape around to secure them. (It helps to use something to hold the front and back panels upright at this point.) Now put the side panels in place and pull that tape up as well. Next, wrap tape around the outside corners (Fig. 20). Make sure that the pieces are all the right size and fit together correctly. Re-trim any pieces that need it at this point with a router or jointer. Adjust the tape as necessary to get the seams as tight as possible. If you have clamps it is a good idea to put at least one clamp in each direction (Fig. 21). Do not tighten the clamps as much as you can, just snug them up so that they are holding the pieces together firmly.

Now take your capillary cement and put it into the bottle with the needle applicator (I squeeze the air out of the bottle and then invert it in the cement allowing it to be drawn up into the bottle). Apply the cement to the bottom joints. I advise squeezing some of the air out of the bottle in the upright position and keeping it compressed when turning it over. This should help control how fast the cement comes out of the needle. (Note that this cement is the consistency of water and is designed to run into the seams so don't go crazy with it. You should see it being drawn into the joints. (It is not a bad idea to practice on some scrap pieces first.) Ideally, this type of cement should be applied in the horizontal position, so if you can put the box on its side to do the side joints (after allowing the bottom to set for 10 -15 minutes) it would be better. If you can't then just run the cement into the joints in the upright position.

After approximately 10 minutes take the viscous cement and put it in the other squeeze bottle. Apply a bead of glue to all of the inside (bottom and side) seams. Apply this glue liberally because the box must be watertight and you won't be able to see these joints anyway (Fig. 22). Let the glue set for several hours.

Once the joints have set, you can remove the scotch tape. Check to see if the box is watertight by filling it with water and letting it sit for a while. Check all of the joints to see if any water is leaking out. If so, dry the inside and do any necessary touchup with the viscous cement.

Installing internal plumbing and baffle

You should read this whole section first and then practice putting the pieces (PVC plumbing and internal baffle) in place so that you are sure of where they go and how to install them before gluing anything.

Cut a 1 ½" length of 1" diameter PVC pipe. Prime it and glue it into the side of the bulkhead fitting that goes inside of the mixing box (the side with the threads that the gasket and nut are screwed onto). Now cut a 45 degree angle on one side of a 5 ½" length of 1" diameter PVC pipe. Glue a 90 onto this piece. Note make sure that the angled end is facing the right way so that it is parallel to the bottom of the box when installed (Fig. 23). Insert the bulkhead fitting through the hole and put the rubber gasket and screw nut on. Only screw the nut on a little bit (Fig. 24). Now glue the elbow onto the piece of PVC which is sticking out of the inside of the bulkhead fitting (Fig. 25). Tighten the screw nut as tightly as you possibly can. Angle the inside piece of PVC so that the bottom is parallel with the bottom of the box (Fig. 26).

Next, glue the internal baffle so that it goes from the bottom of the box at an angle up along the internal plumbing (see Fig. 26). It does not have to be in a specific place but it should run from under the water inlet at an angle pointing up into the first riser. You may want to set the top panel on top of the box so that you can correctly place the baffle before you glue it. (Use the viscous cement.) See Fig. 27 for approximate placement of the baffle. Note: DO NOT install the baffle before the internal plumbing or you will be unable to get the PVC into place to glue it.

After allowing the glue to set for several hours you should, once again, test the water integrity of the box. You may find that a little bit of water leaks out from around the bulkhead fitting (its hard to really tighten the nut enough inside of the mixing box). Don't worry, just drip a little of the capillary cement (or the viscous cement if the gap is too wide for the capillary cement to seal) in the gap between the outside of the box and the fitting. Do Not put any cement on the rubber gasket on the inside of the box.

Attaching riser tube and water inlet chamber to top panel

First, take your ¼" acrylic drill bit and drill 4 holes in the 2" tube approximately ¾" below the flange (Fig. 28). Next, you are going to glue the first riser tube and water inlet chamber to the top panel the same way that you glued the flanges to those two pieces earlier. I suggest gluing the shorter water inlet tube first so that you can put something on it to hold it down while it sets. Then glue the first riser tube to the top panel as well (Fig. 28).

Water inlet nozzle

Get the CPVC ¾" pipe, the ¾" CPVC to ¾" PVC fitting, the ¾" to ½" PVC bushing, the Marine Goop and the other 4" diameter flange (the one with the 1" hole in it). First you will be bending the end of the CPVC pipe so that is shaped like a 3 leaf clover. You have to heat the pipe up (with a butane torch or over the stove) and indent it (I use a chisel) Hold the dent in place until it re-hardens (Fig. 29). Repeat this three times until you end up with the clover shape (Fig. 30). You may have to try this several times until you get the shape right. Don't worry so much about scorching the pipe because you can sand off the burned marks if you don't like the way that it looks. Cut the CPVC about 3 ½" from the end of the clover. Note that in my pictures I cut the piece too short - you want it to stick about and inch or so down into the water inlet chamber.

Take that piece and use PVC primer on the non "clover" end. Also prime the insides of the ¾" CPVC to ¾" PVC fitting and the ¾" to ½" PVC bushing (Fig. 31). Now glue the CPVC pipe into one end of the CPVC to PVC fitting (The flat end not the "clover" end). Glue the ¾" to ½" bushing into the other side. You now have a water inlet nozzle which is ½" PVC (female) on one end and "clover" ¾" CPVC on the other (Fig. 32). As an aside, the reason that I go through the trouble of using ¾" CPVC and converting it back to ½" PVC is that CPVC is thinner walled and, thus, easier to melt and bend into the right shape.

Now take the 4" acrylic flange. Fit it on top of the nozzle (Fig. 33). Use the Marine Goop to glue the nozzle in place and let it set for 4 to 5 hours (Fig. 34). Then flip it over and glue the other side as well. You have to use marine goop because acrylic cement will not bond PVC to acrylic. The Marine Goop may not seem to work at first, but once it hardens it forms a good watertight seal.

Completing assembly of mixing box

This part is pretty easy. You just run a bead of viscous cement around the top rim of the mixing box and set the top in place. I usually clamp it down while it dries to get a nice tight seal. If you do not have clamps you can put something on the riser and water inlet tubes to hold it down firmly while it dries. Before you glue the top, be sure that the larger tube is over the side with the plumbing and that the baffle points up into it (Fig. 35). Allow it to set for several hours.

Installing waste drain on collection cup

Set the collection cup on top of the first riser tube and rotate it until the hole in the flanges all line up. Now mark a spot about 2 inches up on the outside of the acrylic tube on the side opposite from the water inlet chamber. You need to cut a 7/8" hole in the acrylic at that spot. Its best to drill a pilot hole with the ¼" acrylic drill bit and then use a 7/8" hole saw to cut the hole. Note that the pilot bit on the hole saw will hit the internal riser so you will have to use a shorter bit or replace the bit with something shorter (I used a broken drill bit). Take your time cutting this hole and don't push too hard or you can break the acrylic tube. There may be some small cracks around the hole but that is ok (Fig. 36).

Now take the ½" male thread 90 to ½ tube insert connector (Fig. 37) and make sure that the threaded side fits through the hole. (You will notice that it goes almost all the way to the inside riser.) Cut the threaded side down to about ¼" (Fig. 38). Use the marine goop to secure the adapter in the hole with the hose barb facing towards the back of the skimmer and angled slightly down (Fig. 39). Put as much of the Marine Goop on as is necessary to fill the hole and cover the bottom of the fitting. Firmly press the fitting into the hole until the goop sets up a bit. (It may have a tendency to come out a little bit.) You will have to let the Goop set over night before the fitting is fully secured and waterproof.

Final assembly

First, put the larger rubber gasket on top of the first riser tube so that the holes line up. Next, put the collection cup on top and rotate it until the holes line up. (If you marked the sides as I suggested earlier this should be a snap.) Now secure the two pieces together with six 1" nylon screws and wing nuts. Tighten the nuts down until they are snug. It is better if you tighten them like the lug nuts on a car tire. Tighten one and the one across from it etc. This insures that the collection cup is tightened down evenly all the way around. Now put the smaller gasket on the water inlet chamber and line up the holes. Put the flange with the water inlet nozzle on top of that and screw it down with 4 nylon screws and wing nuts.

Cut two 1 ¼" lengths of ½" PVC pipe and get the ½ 90 slip to slip elbow, the ½" slip to ½" female thread fitting and the ½" male to ½" tube barb fitting. Glue one piece of PVC into each side of the elbow and glue the ½" slip to ½" male thread fitting on to one end of the ½" PVC. Put Teflon tape on the male thread side of the barb adapter and screw it into the female thread end of the fitting. Finally, glue the other end of the elbow down into the ½" opening in the inlet nozzle (Fig. 40, Fig. 41, Fig. 42). If you have a ½" slip to ½" female thread PVC 90 then you can just glue the slip end to the inlet and screw the barb adapter into the threaded end. If you are using a larger pump you should put a ½" ball valve between the water inlet and the tube insert.

Get the 1" gate valve (slip to slip) and cut a 2 " length of 1" PVC. Prime the inside of the bulkhead fitting, the 1" PVC and one side of the gate valve. Now glue one end of the PVC pipe into the gate valve and the other into the bulkhead fitting. That's IT!! You are done building the skimmer!

Water Pump Choice

I based the measurements of this skimmer to work with a pump putting out approximately 700 gph. Specifically the MAG 7. (The cheapest place that I have found Mag Drive pumps (and other water pumps for that matter) isBigals Online). It is a good pump and conveniently comes with a ½" hose barb outlet adapter. (You'd be surprised at how many pumps do not.) However, any pump in that general gph range will work. I would not use much smaller because the skimmer would not be very effective.

You can definitely use a bigger pump. The first one of these that I built I set up with a 1200 gph pump. (Via Aqua 4900 from Bigals Online - It costs about the same as the Mag 7 and you will get better performance from the skimmer.) It has a ¾" barb outlet so you will need to use a ½" male thread to ¾" barb on the inlet (US Plastics has these as well). Important: If you use a larger pump like this you must incorporate a ½" ball valve into the inlet side of the skimmer so that you can dial back the water flow when necessary (Fig. 43). The larger pump certainly makes the skimmer more effective because you can better control the waste output. Thus, if you don't already have a smaller pump I recommend this option.

Set Up

If you are placing the skimmer next to an acrylic sump I find it easiest to glue a short length of 1" PVC into the outlet side of the gate valve. Then glue a piece of 1" PVC into the outlet side of the bulkhead in the sump. You can get a PVC 1" union at any home supply store - this piece will allow you to screw the two pieces together so that the skimmer can be removed from the sump easily (Fig. 44). Just glue one side of the union onto the PVC sticking out of the skimmer and the other side onto the piece of PVC sticking out of the sump. If you are placing the skimmer in your sump just glue a short length (depending on room you have) of 1" PVC into the outlet side of the gate valve. Note: It is helpful to fill the skimmer with water before putting it in the sump or it will float.

You may have noticed that this article does not include directions for a cap to the collection cup. If you want to do so you can make a flange on top of the collection cup. I find that to be a bit bothersome (unscrewing the screws etc). I just set a piece of scrap acrylic on the top of the collection cup. This will prevent splashing and it helps the foam to fall over into the collection cup (Fig. 45).

Next run a piece of ½" tubing (or ¾" tubing if you went that route) from the pump outlet to the skimmer inlet. Make sure to clamp these connections down tightly or the hose can come loose. I suggest plastic tube clamps which are sold by US Plastic for the pump outlet and you can probably use a metal band type clamp on the skimmer inlet. Now run ½" tubing from the waste collection outlet to a container of your choice (Fig. 46).

When you first start the pump to the skimmer make sure that the gate valve is all the way OPEN. If you are using a 700 gph pump you may need to close the gate valve slightly to set the water level so that it is approximate 1" to 2" up the inside of the water inlet chamber. The first riser may not fill with foam at this time. Do not set the water level higher yet - sometimes the skimmer can take a day or so to start really producing foam. At that point the you will lose mostly water (as opposed to waste) if the level is set too high. After a day or so, if the foam is not being ejected into the collection cup, close the gate valve a little bit to raise the water level. If you are using a larger pump (1000 gph and up) you will most likely leave the gate valve open all the way. When you turn the pump on you will probably have to use the ½" ball valve on the inlet side to dial the water level back a bit. (Note that by dialing back the water you are creating back pressure in the inlet hose - thus, it is imperative that the inlet hose be clamped securely) Again, set the water level so that it is around 1" to 2" up the inside of the water inlet chamber (Fig. 43). After a day or so you may need to adjust the water level up or down a bit to get good foam ejection. Be conservative - if you set it too high the skimmer will empty your sump into the waste collection container. You are looking for the waste to be a nice dark color - that means you are getting rid of waste products without wasting too much water.

Cleaning this skimmer can be a bit of a pain - you have to remove the six screws to get the collection cup off. However because the waste drains into a separate container you really don't need to remove the top very often. I tend take the collection cup off and clean it, and the inside of the first riser, maybe once a month.

Well That's it! Happy building!

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Original publish date
Jun 8, 2003