I have a 10 gallon tank (first tank ever had) and I now (after killing 5 fish) have started over clean tank, clean gravel, tap water(ammoia=0,PH=7.2),now I add one fish (blue gerammi), one week later ammonia=0,PH=8.6???????? why do I need to do to keep PH in check? I have tried PH 7.0 and it only seems to make the fish impossible to see and a week later PH is right back up ??????? HELP