Speedracking,
Sorry for the confusion. A sump/fuge is external to the choice of glass or acrylic tanks and is a highly desired option but is not manditory.
Using a sump allows you to add water volume, keep most of the hardware out of the main tank (you will still want additional circulation) and make maintenance easier. For an octopus tank it also has the advantage of making a secure top a simpler task.
In order to have a sump you will have to pump the water back to the main tank and dump the water into the sump (or visa-versa depending on which tank is the highest). Most setups have the primary tank at eye level and the sump below for convenience and hardware placement (the recirculating pump has to go in the lower tank, most everything else is an option), however, the original refugium concept was to have the refugium above the main tank and allow small food (pods, small shrimp, etc) to exit via the overflow (they don't tend to survive as well going through a pump and don't automatically get to the main tank at all if a sponge filter is used on the recirculating pump). The idea of a sump is to accept water from the main tank and filter the water as it enters the lower container. Costs, space and esthetics has created a hybred of the two combining both concepts into a single tank setup, usually below the primary tank. Two of my tanks have hang on filters in the sumps and two filter the water as it enters the sump. Filtration options abound
In order to get the water to the sump, you will have to create some kind of overflow that will let a limited amout of water "spilled" into the lower tank (limited because you don't want to drain the main tank in case of a power failure). The receiving tank must have a pump to return the water to the main tank and enough "dry" space to accept the amount of water that will drain from the upper tank when the pump is turned off (both for maintenance and power failure). There are two primary ways of creating the overflow.
The highly preferred way is to drill a hole in the upper tank that will accept a screwed in water tight fitting (bulk head) that accepts a flexible tube. If a tank is designed for a sump (reef ready), it will usually be drilled on the bottom or low on the back and be surrounded by a sealed overflow that limits the amount of water that can exit the tank. If you are converting a tank the more common approach is to put the bulk head near the top of the tank and screen it off to prevent critters from accidentally exiting the main tank. Here again, options abound and our own conversions are inventive
but work satisfactorily.
The alternate is fraught with problems. I can all but guarantee you will only have one tank with this setup but it requires mentioning. In stead of drilling a hole, you can buy or make (that DIY thing again but look up a design and
understand the full concept if you choose to make one, they are not just a j tube for a reason) a siphon box that hangs on both the inside and the outside of the upper tank. In theory, once you start the siphon, it should hold and continue to drain the tank unless the water level drops below the desired level. In practice, the siphons break on a regular basis and has to be restarted so often it becomes unmanageable. There are a couple of commercially available units that incorporate a pump to automatically restart the siphon but I have not experimented with them. Once was enough!
I hope I have not added to the confusion I started
and have at least given you an idea of what to investigate further. Picking up a book on setting up a saltwater tank is invaluable (hint, look for one that mentions sumps and refugiums in the table of contents or in the index and spends multiple pages on the discussion). Getting a range of personal experiences from forums that specialize in saltwater tank setups is an additional (but not alternate) great source.
PS Greg, I didn't see your much shorter version until after I completed my verbose duplicate.
to TONMO! And hey, I think you're the first person who's actually mentioned visiting as a direct result of the TFH issue!
