Honestly what you need to do is get rid of all the fish that don't belong in your tank. Then do lots of water changes and realy that's all it takes. Also answer the questions Leslie mentioned earlier and listen to Wilder. 
Also, I just noticed that you said your angel had pop-eye... I wish I'd seen this earlier. You can't treat internal bacterial infections with melafix or pimafix and this is probably what is killing off your fish. You need some kind of antibiotic, prefferably something you can add to the food. Are any of the other fish showing ANY signs of lethargy or symptoms like your angel did? If yes, treat them immediately but not with melafix/pimafix. Symptoms would include signs of bloat, lethargy as I said before, pop-eye, pine-cone scales, lack of appetite etc. All the usual stuff.
Ferris - Bala sharks need to be in groups of at least 3, are very active, grow to 12" and need at least a 100 gallon tank (125+ prefferably). Common plecs grow to 18". That's what's wrong with the selection.
Also, I just noticed that you said your angel had pop-eye... I wish I'd seen this earlier. You can't treat internal bacterial infections with melafix or pimafix and this is probably what is killing off your fish. You need some kind of antibiotic, prefferably something you can add to the food. Are any of the other fish showing ANY signs of lethargy or symptoms like your angel did? If yes, treat them immediately but not with melafix/pimafix. Symptoms would include signs of bloat, lethargy as I said before, pop-eye, pine-cone scales, lack of appetite etc. All the usual stuff.
Ferris - Bala sharks need to be in groups of at least 3, are very active, grow to 12" and need at least a 100 gallon tank (125+ prefferably). Common plecs grow to 18". That's what's wrong with the selection.
