Fish.

Question
Hi.
I have an aquarium for last 6 months and I've many fish(approximate. 30 or so). The size of the tank is 4feet in length, 2.5 feet in width, and 3feet in height. I've 2 types of bottom cleaners (1 clown plecos and 1 catfish), 8 pairs of gold fish of different types,4 pairs of tetras(out of which 2 pairs are of silver dollar and the other 2 are black in color), and 2 pairs of sharks(catfish)(1 pair is black the other is pink),and few more are there. The problem is that my fish have started dying after such a long time, sometimes i find their fins eaten or they are totally eaten by the other fish, sometimes i find white spots on their tails. I've used all kinds of medicines for their treatment but it works for few days only and i am also concerned that whether I've right collection of fish in the tank or not? I clean my tank every month with the proper procedure. But still I'm losing fish HELP!
I live in India

Answer
Hello. Well first off goldfish and sharks are not a good mix! I have a feeling thats where your goldfish are disapearing to. I suggest you immeadiatley remove the other fish from the sharks. There is nothing wrong with the water. If you have anymore question feel free to ask me.
corinna