Emergency, help please, goldfish with severe fin and tail rot.

[Kittivong]

I've had this goldfish for 1 year and 3 months now. Hes in a 200L tank with 6 other tank mates with him. He has fin rot and tail rot for about 3 weeks now. First time hes had it with a white edge I did a water change and I cured it with tablets called tri sulfa tablets. Later on hes developed it again. That time our ammonia levels were .2ppm and 6.2PH. Yeah, thats a lot. I did a 2 20% water changes in a week. It was pretty mild and his fins and tails started to go away. I added melafix for 2 days. Then went back to the tablets and dosed on the amount at a severe infection.
However it didn't work at all. It was getting worse. As I did the water changes I added aquarium salts to add minerals and also Seachem Prime. Went to the pet store today and checked our water, amazingly our water was perfect.

Ammonia - 0 ppm
Ph - 7.2

I didn't know about the nitrates and nitrites. I also added a heater to 20 degrees Celsius. Help me please, do I just leave it as it is or add tablets or melafix? I'm not sure. I mean he is swimming around but he has not ate for 8-9 days now. Please help me guys also there is some black marks on him.

 

[lauraf]

I'd keep up with large water changes, and meanwhile find out about your nitrite/nitrate. I'd suspect of your ammonia is indeed 0 then your nitrite is too, but your nitrates may be high. And double check that your ammonia really is 0.
If you've increased the temp, you need to make sure the water is being properly oxygenated. You might want to put a bubbler or extra filter in to increase surface agitation.
I'm usually of the opinion that pristine water conditions will cure a lot of fish problems. It makes it a lot easier to keep your water quality high if you have your own liquid test kit - would be a worthwhile investment

 

[CAPSLOCK]

I wouldn't add the strong antibiotic tablets unless you're seeing something specific that they would treat - the same as you don't just take antibiotics for a cold or a cut. Also note that antibiotics kill bacteria, often including the good bacteria you want to keep your tank cycled and healthy... probably why your test showed ammonia after you had dosed it.

Melafix won't hurt anything even if used on perfectly healthy fish, and doesn't kill the bacteria. I'd use the melafix according to the directions, and other than that keep the water clean by water changes as necessary.

Note that if you run (fresh) carbon in your filter, it will absorb things like medications and make them less effective or ineffective.

You could maybe try something especially enticing for him to eat, like brine shrimp or something, to try to whet his appetite. Are the other fish eating?