If a skimmer has been cleaned in several years could it started to cause problems with PH. If you saw my previous thread on Low PH. I was getting a PH of 7.5 or lower. After attaching a airline from out side it went to 7.71. That only lasted a few days. It started to go back down. I decided to breakdown the Protein Skimmer and clean it, since it hasn't been cleaned for several years. It wasn't that bad but still needed it. Today the PH is at 7.83 and the skimmer seems to be working better. I'm still tuning it in.
Before and after pictures:
Before and after pictures:

