Sorry TA, the pH will not stabilize as you start converting nitrites to nitrates. Nitrates are commonly present in our tanks as nitric acid, which will of course drop your pH unless you have adequate buffering capacity to prevent it. If you are having trouble with pH during a fishless cycle, the easiest cure is to add a little sodium bicarbonate, also called baking soda and found in most kitchens. Each bit od bicarb will absorb so much nitrate before it will let the pH move down. The highest pH that it can induce in your tank is in the low 8s so it is perfectly safe for cycling a tank. I don't like to use it once a cycle is complete and there are fish in a tank because it causes such rapid and large pH changes. To control your pH on the high side once you are cycled, place some calcium carbonate, readily available as crushed shell or crushed coral at the LFS, in you filter flow path. It dissolves slowly raising the pH of the tank water and giving it a bit of resistance to pH changes. If you go down that path you will need to measure the pH effect and determine experimentally how often and how much water change is needed to keep your fish in a desired pH range. Unless it is absolutely necessary, I would avoid tinkering with pH when there are fish in your tank.
