NO3...0, NO2...0,GH...25,KH...40,PH...6.8, I don't have an ammonia test. They are on just Goldfish Flakes...I really don't know what Im doing. I started with a 5 gal. and have gotten up to a 15 within this last year. What size should I have and if I do a 20% change, should i condition the new...