Most of the time Ph goes one way. Once it is set it's normal to climb most of the time more so then drop. so you can use the Milwaukee Ph system that uses tank CO² to control a fish tank. It also works for controlling res tanks too. You set the Ph you want to maintain and you get a digital reading. Makes keeping track of Ph easy.

You can get them from eBay. Again it cost money the setup is around 350 bucks.