He has 36" front to back to do what he wants. All he does, for the most part is sit in one spot for days and days, for so long that algae grows on his odontodes. Usually I have one light off, one on and he sits in the dark and the other half in the light and that's where the algae growth comes from, his other side has no algae or very, very little. For 3 days I had him in a 220 that is 23" wide on the inside, this guy is 23", he is better off in a 36" wide tank rather than being squished in a 23" wide tank. Every few days he changes to a new spot, sometimes under the light that is off, sometimes right in front of the 3200 gph wavemaker and sometimes he moves the wood and goes behind it.