sick silver shark

Question
Our silver shark has become inactive recently, and it has light patches on the side of its body. These patches have started growing what looks like white mould or fur coming out of his scales. We also noticed that some of the smaller fish were trying to eat the mould. We have cleaned the tank out, but don't know what else we can do for him?

Answer
Hello...
What did you mean when you say you cleaned the tank out? Did you take out ALL of the water and clean out the gravel? If so, that is a big no-no. When you take out everything you destroy your beneficial bacteria, and your tank has to re-cycle all over again. Some fish cannot handle the cycling process as there are a lot of ammonia and nitrite spikes. Not only that, but it can take anywhere from 3-6 weeks for a tank to become established. I definitely suggest doing research on the nitrogen cycle - it is important for every fish keeper to know.
As far as the fungus, it is most likely due to poor water quality. You should be doing 25% water changes once a week. Also, since you have a fish that grows a little over a foot long - your silver tipped shark which is actually a kind of catfish - I hope you have at least a 30 gallon tank. Larger if you have several other big fish in there. And remember they are territorial, so they need a certain amount of space to themselves.
You can treat him with melafix and pimafix, they are anti-fungal and anti-bacterial all natural medications, and you can combine them to create a sort of remedy-all that won't deplete your beneficial bacteria.
So, read up on that nitrogen cycle so you can be a better fish keeper, and work on getting a larger tank if you have anything under a 30 gallon.