Ok - so my goldfish has something wrong with him and I cannot identify what it is. There's nothing physically wrong that I can see - he look fine. Before you ask - his 20 gallon tank is fully cycled - haven't had ammonia or nitrites in a long time. Just checked again and they are zero. I have had problems keeping the nitrates down - so I've been doing water changes 2x weekly. Not sure how to keep them super low or if that's even possible. For the last week he's started hanging out along the bottom, not swimming around much, not flapping his fins much, and almost seems to sort of drift along with the current created by the pump. Kind of like he starts floating up (rear first), flaps his fins to keep himself down, and repeats. The only other new thing I've noticed this last week is he's doing 1 of 2 things. Either throwing up or going to the bathroom. I've been finding reddish brown things floating up top that sort of look like little tubes...segments of a worm? Not sure how to describe them. But a few times I also found basically what looks like tiny clearish white sausage casings with a white stringy thing trailing off the end floating around, too. I do not know if that is normal - if I just happen to be catching it when I get up or come home and usually the filter takes care of it - or if this is new. I did actually see a tiny squiggle of reddish brown detach from between his belly and fin - way smaller than the stuff I've been finding floating around - so i'm not sure if he's going to the bathroom and spitting stuff up - or none of the above. And no idea what the white-ish stuff is. But he continues to lurk at the bottom, slowly moving when he does, not swimming much. Skipped feeding him yesterday and today gave him a few pieces of green peas. Any ideas on what might be wrong? I would appreciate any advice because I have no idea what to do to make him feel better. Thank you. Oh, he's a few inches long and has a 50 gallon fluval pump going that contains the sponge, carbon and bio-media. Thank you.