The tank is 8 by 2 by 2.. just removed what I think to be 5 males. The big boy is starting to move around and explore the tank. He was not as active before hand. Still have 12 in there. 5 are on the small side.. thinking of removing the 2nd male and the second cave give the dominant male more room... he is a fair bit larger than the other male. I'm sure I've missed some males. Venting is tricky