Best "shape" tank for octo


Mar 26, 2009
I'm looking at buying a new tank..or 2..1 for octo and 1 a larger reef. For the octopus tank I see size recommendations for gallons but I was wondering what the best shape would be. I've been looking at tanks from 70-110gallons all in different shapes i.e. cubes, ones that are considered tall, and I was wondering what would be the best for an octo tank. I was thinking that length and width would be more important than overall height but wanted to see what you all thought.


Staff member
Moderator (Staff)
Sep 4, 2006
Good question and I am not sure there is a good answer. Most keepers will suggest length over height but even the hummelincki needed a minimum of 2' to "stretch" out an arm so a propagation tank is not a good idea. Beldar (macropus complex with two very long arms) also needs at least 2'. Anything taller than 2' becomes a problem with maintenance even for longer armed folks (my 3' 140 reef is a royal maintenance pain!).

My hummelinckis would occassionally bump into the tank walls of both the 30" tank (too short if you have other options) and the 50" (this has a dividing set of tubes so the width is only in two place) but the macropus (much smaller body, much longer arms) never ever bumps into the walls of a 2' diameter hex. The mercatoris in the same tank were never observed bumping into the walls but they rarely swim (the macropus often does a short swim and makes the turns with ease but this may be the octopus rather than the tank). At one time it was thought that octopuses could only be successfully kept in round tanks. This has been long disproven but there may be some merit to the consideration. If there is (second guessing), then a corner pentagon or a bowfront might add some swimming comfort.

Front to back depth has not been discussed much and I have no personal feel for how thin is too thin or if there is an advantage to a deeper tank. With more front to back room, it does allow for a wider sand area but mine have all preferred the LR to the sand.