Please please help!! About 8 weeks ago set up my first tank. 190 litre. I added water conditioner and plants. I waited about 6 weeks and I made sure that ammonia and No2 and No3 levels were zero. My plants were doing fine so decided to add my first fish. I bought 7 sissortails and added them to the tank. As expected the ammonia levels went up briefly and then come back down to zero along with No2. No3 went up to about 0.10. So as the water quality was fine and the fish seemed happy I added 3 orange tail sharks and a pleco. The same day I noticed that one of the sissortails had stopped eating and had pop eye, so I went my local store and bought some treatment - Interpet Anti internal bacteria. Which seems to be working well and the swelling is going down slowly 2 days later I noticed that one of the sharks now has cotton on his gills, but there is a notice on the side of the anti internal bacteria bottle not to use any other treatments in the same tank. I went to my local pet store and was advised to keep treating the pop eye (as the sissortail is still not eating but the shart is) and add some aquarium salt to slow down the progression of the cotton mouth until the sissortail is better then treat the shark But I have just read that I can't add any salt to a tank with a pleco fish. I only have one tank and can only apply one treatment! I can't choose one fishes health over another! I really don't know what to do! Please help!