FIsh Cycle

If you are cycling the tank with fish in it then you need to monitor the ammonia, nitrite and eventually nitrate levels. When the ammonia level starts to get near 2ppm do a water change and get it down to under 1ppm (lower is better and large water chnages don't hurt anything). Eventually you will see nitrites form and when they get near 0.25ppm do a water change to get them down (even if your test registers 0 there is still nitrites present and still enough food for bacteria). Eventually those numbers will stay at a constant zero for well over 24 hours. At this point nitrates form and you should do enough water chnages to keep nitrates below 20ppm.

Right now a stable pH is important, more so than the actual number.