I have read that nitrification will lower the pH. I believe the nitrifying bacteria use carbonates, bicarbonates, etc. when breaking down ammonia / nitrite, and produce acids, and this causes the reduction in pH.
Your pH should not go up. If it is rising it may be due to other factors such as your substrate (what is it?) or decore.
good news my ph has lowered its about 7.2 atm better than the 8 or so it was the other day could have something to do with the "nitrification", also added my big piece of drift wood to the tank a few days ago too!