i have had my tropical fish tank set up for nearly 3 years now,?

[Gareth]

i test the water regular it is always fine (it is a 190L tank) every time i add small fish to it like platy they die but if i put something bigger in there it lives why is this?
in the tank there is 3 xl gourami about 5" ,1angelfish about 4", 3 clown loach from 2" to 4" ,2 neon tetra 1 silver fin etra and a few albino catfish
there are no corpses in the tank i know every fiish that is in there what else could be wrong

 

[Joee]

If you cannot find the whole corpse of the fish, the larger fish may be eating them.

 

[Joee]

If you cannot find the whole corpse of the fish, the larger fish may be eating them.