I think one of my fishs sick

Question
Hi.
  One of my neon tetra (called Rot) might be sick. There's a white spot on it's tail that looked a bit like fin rot. Except for the white spot, which might be growing larger, Rot's great.
  I know that fin rot might caused by poor water quality, so I changed 50% of the water, but it didn't get better; I know it might be caused by stress, so I remove Blackie, a bigger fish that infrequently eat smaller fish, and provide a hiding place, which was a plant; I know it can be caused by germs, but if it was, the other fishes would probally get it too, but Rot (the fish) was there for a long time, and the other fishes are as fine as ever.
  Everythig in the tank's great: the temperture's good, the foods are designed for tropical fishes, the tank's fairly large, the larger fish are friendly (excapt for blackie)...
  So is it fin rot? What can I do about it?

P.S. Rot was the only fish in the tank that got it.

Answer
Hi Helen;

Rot may have finrot, or it could even be tumor or something too. If he is older he will be more prone to such things. You might want to separate him to a tank by himself to help him heal. Just a regular little 5 gallon tank set up as a bare "hospital tank" will do. Only lights, airstone hooked to an airpump and a heater is what is needed. No gravel or decorations. Change 25% of the water in the hospital tank every day and siphon out any waste you can see. This will keep it clean and he can hopefully recover on his own. A bare hospital tank is ideal for using medicines in too if he needs it. If you use medicines in a regular tank, it can cuse cloudiness, discolored water, the gravel and decorations and filter absorb medicine. It medicates fish that don't need it and it is also much more expensive to treat the main tank. Medicines are dosed by the gallon of tank water so you will need a lot more than you need for a little hospital tank. It's just better if you don't have to do that.

Keep him in the hospital tank for 3 or 4 days and if he doesn't get better, go to your local fish store to see what they have available for fin rot. Treat according to the label directions.

Below is a link to a web page with pictures of fish that have various diseases and ailments. See what you can find there that looks like what he has while he is "in the hospital";

http://www.fishpalace.org/Disease.html

I hope he feels better soon......

At Your Service;
Chris Robbins