Hello. Thanks for getting back to me. The ammonia, nitrate, and nitrite levels in the tank and my tap water are all at 0. PH level in tank is about 7 and same for tap. I use API test strips to test. My tank temperature is at 80 degrees. My tank is about a 40 gallon and has been running for about a year. The filter is an aqueon hob and is rated for a 50 gallon. I change the water every 4 days and do a 50 percent change every time. He is due for one today. I have three fancy Goldie's in total. Pudge, and two smaller ones. Water conditioner used is big Al's step one. I feed them omega one sinking pellets twice a day. No new fish added. Pudge did have ammonia poisoning about 6 months ago but we're almost past that now, he only has a small spot left on his tail. I used antibiotics for the tail and I use aquarium salts regularly. His behaviour is normal, eating and swimming as usual and I noticed today that the spot under is eye appears smaller. A fish expert at big Al's said it may be a ruptured cyst. Thanks again.
As well, I tried posting a photo before but the site won't allow it because it's too large.