Hi tez,
Welcome to kokos!
Black is often a sign of healing from a chemical burn--do you have test kits to check ammonia, nitrite or nitrate levels?
There is a box above with lots of questions--it will help us if you can answer them as best you can.
Since you have had the fish for a year, you are doing something right.
Partial water changes using a water conditioner (to get rid of the chlorine) are the best way to start.
When we have more information from you, we can better help you.