Goldfish black all over

Question
I have a cross bread goldfish in a tank (5 gallons). Before, it was in a fish bowl and got ammonia burns. Now the tank is replaced to the tank. It doesn't look good for more than a week. I hadn't since the burns. The blackness had spread throughout its body. Now it had a dull blackness(in its fins &body). 85% water changers (tap water is kept for 24 hours to settle chlorine) are done everyday(or every other day) and an air pump is there. It hadn't eaten much(there are some plants in the tank which it might feed on- I'm not sure) Its belly is not flat but round(not huge). Today i saw that tip of its bottom tail fin has whitened, transparent and damaged. The ammonia dark patches are still there. I checked the water for ammonia and chlorine but they were fine levels. Its alone in the tank, often scared and stays in a corner (very lethargic). Body is covered in darkness (not black spots but simple splotches-more like suit/ash) They don't look like fungus(they don't come out of the scales).
I add a pinch of salt after every water change; there is no filter.
Reply soon Thanks Km

Answer
Hi Kim,
Sorry that you are having so much trouble with your goldfish, and I think I can really help you. The bad thing about goldfish is, they are very dirty. Not in the sense that they look gross, but they do poop a lot, and they fill up a small tank with ammonia very quickly.
If he were to be moved to a 20 gallon that would be the best. You can buy a cheap 20 gallon tank from Wal-Mart.
As far as your fish turning black, this is actually quite common because color pigments in goldfish are pretty unstable, though sometimes fish also change color or pale when they are sick.
Another problem I noticed is that you don't mention adding water conditioner (dechlorinator) to the tap water. This is bad because even though chlorines can dissolve after around 24 hours when left to sit,  chloramines take several weeks to dissolve, and are even more toxic to your fish. Chloramines are a mixture of ammonia and chlorine, and too much over time can be fatal. So I suggest from now on using a water conditioner. They are not very expensive and will prolong the life and health of your fish greatly. Especially the ones that add slime coat.
As far as water changes, 85% is a bit much. You should be doing no more than 40 percent. The reason is when you go from a high amount of ammonia or nitrates/nitrites to none at all it can actually shock your fish's system. So do smaller, more frequent water changes instead of large ones once in a while.
Last but definitely not least, it's very important you add a filter, because of what I told you before - goldfish are dirty and produce twice the ammonia that other fish do. Especially in such a small tank, it is going to be hard to keep him alive for very long.
Get a decent filter, (such as a bio-wheel), switch to a 20 gallon tank, do small frequent water changes, and start using tap water dechlorinator with slime coat, and your fish will become much more healthy, and live a lot longer. (Goldfish are supposed to live for at least 12 years!)
Best of wishes.