He got better after I wrote this, then he got sick again. Sigh.
Yes, the tank is heated. It used to be 74 and now its 80F. Goldfish are tanks, they can survive any temperature, it'll just shorten their lifespan (I've read cold 20++ years, at 80-85 more like 7-10).
The water is very clean. I do 75% water changes weekly, I've never had nitrite or ammonia above 0, and my nitrates are always below 1-2 (ie, no color change in the API test kit, which is not sensitive below that). The tank is way oversized for the size of the fish in there, so there really isn't a large bioload. The reason I was doing so big of changes is the driftwood was leaching a lot so it turned brown. That doesn't happen much anymore, but its just habit now.
