Silver Dollar with internal swelling

Question
Hi Chris!
Instructions:
29g-set up for 3.5years.
2- silver dollars, 2-kribs, 4-corys, 2-tetras, 1-bushy pleco
AC200(sponge,carbon,ceramic)AC150(sponge,wool,ceramic)
pH, ammonia, and nitrate levels - I ashamed I dont know.
I change 5gal of conditioned water a week with a gravel vacuum syphon and add "cycle" each time. I change 10-gal every third time to get a good vacuum. Tank is clear all the time.

OK, first, my silver dollars are ten years old...But, I feel I owe them more than just euthanizing If I can help. One fish has a large veritically oriented internal swelling in the back half. He behaves and eats normally - last feeding seemed to eat voraciously. Swelling was noticed about two weeks ago and has gotted progressively worse fast. I will give you a link to a forum posting so you can see some bad pics I took (sorry my cam stinks). Thanks so much Chris for your timely respone as I dont think he has long.  Mike

http://www.aquaticcommunity.com/aquariumforum/showthread.php?t=4587

Answer
Hi Mike;

Fish can be very difficult to photograph can't they? I could see him pretty well once I used a photo editor and brightened up the image. It still wasn't clear but at least I could get a basic idea of what it looks like. It could be an abcess from an infection of some kind. Since he's eating and acting normally otherwise, don't give up on him yet! If you could separate him to a quarantine tank you could treat with an antibiotic that absorbs into the fish. A ten gallon with only a heater, lights and air bubbles is all you need. No filter, no decorations or gravel. These things all absorb medicines and render them much less effective. You also don't want to put medicines in the main tank. That stuff makes a horrible mess in tanks and it's best not to treat fish that aren't sick anyway.

Kanamycin or "Maracyn 2" are the best for reaching internal bacterial infections. You could instead try a medicated food for bacterial infections. That's actually the best way to administer it. You still want to isolate him though. The other fish don't need the medicated food.

I hope he gest better soon...

At Your Service;
Chris Robbins