After 2-3 weeks the charcoal (carbon) is useless, so if it is the original from a year ago, maybe it is breaking down and giving off some sort of cloudiness. There are natural ways to raise your ph, do a search on here or google, it might be something you want to try (sorry, I always forget, its either peat or driftwood I think?). Most fish can adapt, but I think 5.8/6 is on the low end of what they can easily adapt to.
As long as you can insert a new carbon bag without replacing all of the filter media in your filter I would do that and ditch ALL of the chemicals for a couple of weeks and see what happens. Your ammonia should read 0 all the time, unless the tank is recycling for some reason, you are overfeeding, overstocked, not cleaning enough (gravel vacs.), not doing regular water changes, etc. Are all of your maintenance routines good? What do you do?
As long as you can insert a new carbon bag without replacing all of the filter media in your filter I would do that and ditch ALL of the chemicals for a couple of weeks and see what happens. Your ammonia should read 0 all the time, unless the tank is recycling for some reason, you are overfeeding, overstocked, not cleaning enough (gravel vacs.), not doing regular water changes, etc. Are all of your maintenance routines good? What do you do?