I just got a 2" red severum (my first), still in the hospital tank. This morning I saw him then turned off the pump to feed, then walked away for a few minutes. When I got back he was gone! I llooked all over for him/her, even the floor, and just could not find them. He/she likes to hide under the pump, but it was off and they were not there. It's a freakin' 5g tank with 2 flower pots, a stone and a sponge filter.
So, I gave up, and came back a few minutes later and there he/she was. Can these things hide in the gravel? It's the really fine stuff.