goldfish black spots

Question
Tank has been set up for a few months.Had them in another tank, upgraded to this one. 55 gallon tank, two goldfish, 50 gallon aqua clear filter and a 210 pond pump. ph is 8.2, ammonia 0, nitrite 0, nitrates 5. Change water twice weekly about 20 per cent. One goldfish has had black marks on his belly and side for months and on his fins for months. His fins are shredded. Now months later the other fish has black on his belly and it has spread to his left fin and it is all black and split. I have used salt baths, melafix medikoi and marycyn 1 and 2 in the past. They still have it and it does not go away. Cannot figure it out. The one that just developed it has tiny black spots all over his body too.

Answer
Hi Linda;

The black may be part of their normal coloration or could even be scarring from ammonia burns in the past. The water chemistry looks good and twice weekly water changes are very good. Do they ever pick at each others fins or chase each other? Are there any plants or other decorations in the tank they could be getting caught on? It could even be bacterial infection that is not letting go. If they were in a small tank for a long time before this big one, their immune system may be damaged. Medicated food may help if bacterial infection is the cause. Use it according to the instructions and don't feed any other food during the course of treatment. Keep up the good work otherwise. I hope they get better soon...

At Your Service;
Chris Robbins