• Looking to buy a cephalopod? Check out Tomh's Cephs Forum, and this post in particular shares important info about our policies as it relates to responsible ceph-keeping.

Swtch from fresh to salt


May 2, 2007
Hey ya'll. I got your site info from the great articles in TFH. I have 4 freshwater tanks. What I need to know is, can I change a 75 gal freshwater tank into a tank that is suitable for a Bimac? After reading about them in TFH I'm in love. I dont mind taking alot of time to do all the research needed, I'm in no hurry. I've never tried a saltwater tank, but I am very proud of my freshwater tanks as far as care, looks, and no fish dying. I was told awhile back that if I wanted a saltwater tank, that my best bet would be to sell my freshwater tank and get one set up for salt. Can't I just buy what equiptment I'll need and add it to this tank? I have alot of work ahead of me, as the only equiptment that I'm familiar with are heaters, lights, and the hang on tank biofilters. I'm not even sure what a refugium is. As I said, I'm willing to take the time to do this right, but I need to know if I can even use this 75 first. Or, would ya'll recommend me starting a smaller 30 or 10 as a salt for a seahorse or something before I try with a bimac? Thanks for any help... Kristie
Welcome to Tonmo! Usually, we recommend using a new tank, as any sort of medications or even the gravel (high metal content) used previously could lead to an early demise for such a finicky animal as a cephalopod. The trace metals can actually reside in the silicone sealant after any sort of use (ie: ich medicine, etc).
Under the heading of "ceph care articles" up on the top left of your screen, are a number of writings made specifically to help out with first time octo buffs, be sure to check those out !
:welcome: to TONMO! And hey, I think you're the first person who's actually mentioned visiting as a direct result of the TFH issue!
Thanks for the replies

I bought the 75 gal new two Christmas's ago. There has never been any meds, copper or even plant fertilizer in it. I have always quarentined, sp, new fish in a 10 gallon for 6 to 8 weeks b4 adding to a larger tank with other fish. There have been no new creatures added to that tank since last Christmas when I bought 30 Red Cherry Shrimp. All my plants are live and I keep alot of snails in the tank, so between the snails and the highly sensitive shrimp I have made sure not to put ANYTHING but Prime chlorine remover in the tank. I would rather not sell this tank unless I absolutely have to. If I can buy a chiller, different filter ect. I would rather do that. Thanks for any help.. Also, would freshwater snails be an appropriate food for a bimac? I have about a gazillion of these snails. Some are rams horns and the rest are a round type of snail about the size of half a thumb. The puffers that I've had really loved eating them, along with the young snapping turtle that moved into my yard pond.. Kristie
Hello again, Kristie !
If you have been the sole owner, and have never had any metal based objects in the tank, you should be fine with using it.
Re: freshwater snails...I am not sure about that one. With the difference in specific gravity of the flesh, it may not be the best thing to feed the octopus, except for as a treat now and again. Be sure to stay away from goldfish, etc, also !


Try a snail in a cup of saltwater. It may disolve almost on contact or very soon after and wouldn't work out as food if this happens (IF the octopus eats the snails, it won't be an immediate consumption). Some snails are more tolerant than others of salt. The ramshorn might do better but I would test them as well. I used to keep brackish water for my discus and had Apple snails without a problem but the water was not even close to reef salty let alone the full strength salinity needed for an octopus.

Only our reef and octo tanks were originally designed for saltwater, the other 4 have been DIY modified (all are acrylic). If your 75 is acrylic, you may want to have it drilled (or DIY - pretty safe and easy with acrylic) for an overflow to be able to add a sump or sump/fuge. Glass can be drilled but it is risky. Several Tonmo members have had glass tanks successfully drilled but most aquarium stores will not guarantee that the tank won't crack. If one of your 10 gallon (or larger) QT tanks is no longer used, it can be put to use as a fuge and give you a place to put a skimmer, the chiller pump, filtration and anything else that makes octo proofing a tank difficult.

Greg and DW, thanks for the info on the snails. It doesnt sound like the snails that I have will work. DW, this might be a stupid question, but what does DIY mean? Also, are you saying that I wouldnt have to have my glass tank drilled or replaced with an acrylic tank if I use a 20 or 30 gallon tank as a fuge? Thanks to everyone for their in depth answers.. Kristie
If you are going to use a sumped system, I would recommend drilling out holes for the bulkheads...the other option is to use a "hang off the back" sort of thing...big problem with that is octos do love to escape, and the hanging openings just offer another way to get out.

On the downside, if you are going to drill a glass tank, the store you take it to will not guarantee that it won't crack. All of the tanks out here are ordered predrilled from the factory.

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 :confused:

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 :roll: 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 :bugout: 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. :talker:
Thanks for the new info DW. It sounds like I'll be better off selling my tank and getting another. Sorry that it took me so long to get back on here. We have 2 dogs that got Botulism, and its been a mess. I plan to get as many books as I can to learn as much as I can before I start the new tank... Kristie
Welcome to Saltwater

Welcome to saltwater! Yeah it rocks! I just recently made the switch, and while i dont have an octo yet, i do have a very successful reef tank that im very proud of! hopefully an octo tank will happen soon! i have a free 30 gal right now.. but ya, stay in touch!

as to your question, If it is your only option, then it is technically possible... but risky. If you were to change it to salt water be sure to clean it VERY thouroghly and then to cycle your saltwater tank well beforehand.... however i wouldnt reccomment a cephalapod because, as previously states, they are very picky, for lack of a better word.
as a rule of thumb (yes I'm on my favourite hobby horse again :roll:) I would never feed freshwater animals to marine animals. There are problems with the protein to fat ratio's. I would always feed marine to marine.



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