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Tank sizes?

Jul 20, 2010
Why is it so important to have such a large tank?? I keep reading a minimal of 75gallons. Is it possible to keep an octo in a smaller tank, since space is an issue for me? Thank for the replies and help ^.^

Also, how would a seahorse fair inside a tank with an octo?


Staff member
Sep 4, 2006
Octopuses, for the most part, are opportunistic feeders. Seahorses have no defenses and can't even swim well or hide. The outcome for those insistent on trying has been the loss of the horse in a day or two when the octo came across it in its travels.

Tank size is species dependent. However, you can't count on the species that you will get. They don't live very long so you need to be thinking multiple animals, not a single specific one when you decide you want to be an octo keeper. The question and multiple answers comes up a lot and there is an intent to make a recommended tank size sticky from the information in Nancy and Colin's (both staff members) book, Cephalopods, Octopuses and Cuttlefishes for the Home Aquarium.

You can keep a dwarf in anything from a 15 to a 35 but they are nocturnal and not very interactive. I enjoy keeping them along side the medium sized animals and usually have at least one in residence (the dwarf tank is vacant, unfortunately, right now but I have some hatchlings to make up for it :wink:). An aculeatus fares well in a 45 and the smaller version of the hummelincki can be comfortable in that sized tank but hummelincki can get large enough to need a 55 and you don't know what the size will be when you bring the animal home. Briareus need a minimum of 65 gallons with a good sized sump and may outgrow that at the end of their lives.

Part of the reason for the larger tanks is water quality vs food intake and part is room to move around. The larger the animal, the larger the food intake and the greater the issues with keeping the water quality in check (zero detectable ammonia and nitrites are required).

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