fish tails being eaten over night

Question
hi everyone need help with my tank 165litre tank last water test is 7 and temp78 having problems with fishes tales being eaten during the night got a long arm shrimp, humebug cat fish and Malaysian cat fish, harlequins and neon tetra i also have some gouramis but its the smaller fish that is being eaten and its only taken one a night but not eating the hole fish and leaving it alive please help had my tank set up 4 about year and a half many thank tracey

Answer
Hi Tracey:  One of your cat fish are trying to eat the smaller fish. At night fish settle to the bottom of the tank to rest where they become prey to other fish.  Treat the surviving fish with malafix and separate the catfish from your smaller fish... dave