Sick goldfish?

Question
I have a black moor who has now lost her colour and turned orange. Recently black has appeared on the ends of her fins and they are going ragged. The other two fish in my tank do not have this problem so i have no idea what is wrong with her!?

Answer
Goldfish change colors often because their color pigments are unstable. However if her fins are looking torn that is a bad sign. Make sure you have a large enough tank. With a goldfish you need at least a 20 gallon tank, plus ten more gallons for each goldfish thereafter.
Since you have three, you should have a 40 gallon tank.
If you already have a large tank (30+ gallons) then it may be your water quality. Test for ammonia/nitrites/nitrates and see what the readings are. It's possible you just need to do more water changes.
Remember, the bigger the tank is, the easier it is to keep the fish alive!