You should never try to manually mess with your water PH by using chemicals. It will do more harm than good. Leave it alone and stay away from "PH up" or "PH down" or any similar products. They are dangerous for aquariums.
What is the PH of your local tap water?
PH should not have gone up. It should have gone down instead because of the build up of nitrate. Nonetheless, 8.0~8.2 PH is still perfectly fine and you should not worry about it.
On the other hand, acidic PH (below 7) might slow the bacteria growth, and at below 5~6 it might stall the cycle, because the bacteria do not like acidic environment. When that happens, it's time for a partial water change.
