sick freshwater sharks

Question
I've had my tank set up for at least three years. It's 30 gallons. We have about 13 fish -- six tetras, two bronze cories, a loach, a bala shark and a couple of good-sized red-tailed black freshwater sharks. I use a 30-gallon filter attached to the back of the tank. I change about 10 gallons of water every two weeks, and I've had a very healthy tank thus far.

My question is that my two black sharks have been sick about three weeks now. They have some sort of fungus and we can't figure out what it is. It's white, grows below their scales and it looks a bit like cotton. It grows in small patches/makes their scales appear white. Nothing we've done to treat them has worked. We've tried Maracyn, Pimafix and Melafix. And although with the Pimafix, the infection got better, it's still not gone away. In fact, with our smaller shark, it's reared up a little again. I'm at a loss for what else to do.

Please help.
Chris

Answer
Hi Chris;

Redtailed sharks are very territorial with their own kind. There really should be only one per tank. They are biting each other and the injuries are getting infected with fungus. You can provide additional hiding places but the only permanent solution is to move one out. Maybe another tank or find him another home. They can't help themselves. It's just their nature.

Use an antifungal medication to treat it. Your local fish store should have some. The problem is, many if these  medicines color the water, stains decorations, equipment and sealant blue, and can mess up the biological balance of your tank. It's best to use hospital tanks. Or, use one ten gallon hospital tank and use an aquarium divider. They would kill each other if you tried to put them together with no divider in anything that small. You need only a bare tank with a heater and an air pump with air stone. You don't want to put a filter or any gravel or decorations in there. They absorb the medicine and make it less effective. Change 25% of the water daily so they heal fast and it keeps the tank from developing waste toxins since there is no filter.

I hope they feel better soon...

At Your Service;
Chris Robbins