Please help my goldfish

Question
I bought 2 goldfish, 1 died about a month later, I waited a couple of weeks and then bought another. He seemed fine until I noticed a white lump on his head, this disappeared in a few days, then he had an even larger lopsided lump, he started to lie on gravel, I isolated him for a week and he seemed to get better and the lump disappeared. He went back in with the other fish and seemed ok, but after a few days he started rolling in the water, floating upside down and lying on his side on bottom of tank, I thought the lump had caused brain damage but my friend said swimbladder, I got the necessary treatment but it hasn't work, he seems to be worse, I feel so sorry for the little guy, he just lies at the bottom looking around and I have to swirl food down to him. I do everything correct as far as I know, weekly water change of about a 3rd of water, always leave the water overnight and use the water cleanser, have a filter which I clean in the old tank water. I just feel so sorry for him, I can't kill him, but I don't want him to suffer either, do you think this is brain damage or swimbladder? Is there anything I can do for him, he seems like a fighter, he has been hanging on in for weeks.
Thanks

Answer
Hi Janice,

The lump on your Goldfish's head was Lymphocystis - sometimes fish die from it, others make quick, mysterious recoveries.

It is currently suffering from Swim-bladder trouble. This condition is usually restricted to deep-bodied fish (like Goldfish) although scaleless fish also seem to be susceptible.

Unfortunately there is no known cure for this condition. It is accelerated by coldwater so a gentle temperature increase will relieve the symptoms along with a mild salt bath. Try feeding Daphnia or worms to aid digestion and thus relieve the symptoms further.

Good Luck

Tom