Get the fish in a bigger tank.
Do some basic research on the fish species. You don't put platties and clown loaches in a tank with a managuense (a) and (b) in a tank that is too small for the managuense let alone other fish.
Ignore suggestions to give your fish meat...chicken, beef heart...whatever. That's just a BAD idea. Uneaten food fouls the water, and there are plenty of REAL foods to feed your fish without having to shop at the deli.
If the fish doesn't feel comfortable with his surroundings...say, because the tank is too small...they will hide. Second...this particular species spends a lot of time in hiding. It is an ambush predator.