Fishes disappearing from fish tank?

You didnt say the size of the fish. Are they babies or adults? Try lowering the water down to almost nothing... they may be hiding in the plants/gravel. Or check your filter setting, they may be getting sucked up. Guppies & Tetras are good community fish.... if the above dont help i would try removing the clown loaches from the tank. put them into a quartine tank and closely monitor both tanks.