I have my mantis in a 2.5G and he is absolutely fine. He is getting moved to a 6G in the next month...Three times the living space...he'll be very happy. If things don't work out with the sale, even though it is a smasher, if the offer from FF13 for the 8G tank still holds, I will be able to care for him. Obviously, I'm fine with not taking him, but if the other deal falls through...at least he will have a home.