discus troubles

I have 6 discus ranging from 9-14cm. The tank is 165 litres, I'm going to upgrade them within the next 3 months. The smallest guy has a very thin head and body, and one of the bigger guys has bloat. I have used Epsom-salts twice now and neither fish seem to be improving. I used 10 teaspoons...

I don't want to be like other people and say Discus are not for me , but maybe it's true. This is the tank setup. 65 gallon Heavily planted Canister filter Heater 50% water change once a week Clean the filter once a month This my problem. I have 2 Synodontis Catfish live in the tank for like...