My black moor goldfish sits at the top of the tank with his tail bent and head down. He doesn't swim around much. When food is put in, then he moves for that. I noticed where the tail is bent, it looks white. He is all black. Any suggestions?

try putting a scoop of aquarium salt into the tank, and see if he perks up. Also don't feed flake food all the time, he will get constipated.

Well black goldfish do have a tendency to lose their black but they usually go red/orange first before white. This could be finrot but without knowing more about the symptoms I can't say for sure. Finrot looks like a white fuzzy bit on the edge of the fins, and as you can tell by the name, it causes the fin to rot. This can easily be cured by treatments available at most pet stores, but you should ensure the water is of high quality so it doesn't keep happening.

It sounds like at the moment he has a swim bladder problem, this can be caused by a number of things- firstly an infection caused by poor water quality. The first thing you should check is your water quality. If you don't have a test kit, get one! They are totally essential.
Your ammonia and nitrite should be zero and your nitrate should be less than 50ppm and the pH should be around 7 for goldfish.

Swim bladder problems can also be caused by constipation. Fancy goldfish are especially prone to this because their gut is more compact. A quick and easy remedy for constipation is to feed him a shelled defrosted pea, all squashed so he can eat it. This should get his guts moving.

The third thing that can cause swim bladder problems is genetics. Sadly the quality of livestock available in pet stores is pretty poor, so the chances of getting a fish that is a bit weak and prone to illness is pretty high. This is no reason to quit though! It just means you have to be extra-careful in providing your fish with the right environment. Give him plenty of space, a good diet and lots of filtration and he should be fine. Here are the basics if you're not sure- http://www.practicalfishkeeping.co.uk/pfk/pages/show_article.php?article_id=418