Aquarium in Low Conditions

Unfortunately my aquarium is encountering some even more serious problems. It has levels of ammonia, nitrite and nitrate which is very bad. Ammonia is fish waste but I think nitrite and nitrate is a harmful chemical. Anyway, any level of ammonia and/or nitrite can be lethal to the fish. I have tried many solutions for curing this but none of them worked, in fact its getting even higher levels. Maybe I used the wrong solution, maybe I overcrowded the tank, I don't know. All I do know is I think this caused some of my fish to have fin rot and I can't find a proper solution for it. Only to add on to the problems, my pH level is 8.2 and every week it gets higher by 1.2. So in just one week my fish developed fin rot, it has moderate levels of ammonia, nitrite and nitrate and my pH is 8.2! It should be 7. Again, any help is needed and would be greatly appreciated. So, whether your a novice or pro at the hobby I ask you for help with this.
Goodbye,
Birdman