between doing water changes which helps to stabilize ph adn having your powerheads pointing at the waters surface you shoudnt really have any swings.
BUT I also had a similar issue and it was the air in my house. I used to run the air 24/7 which didnt allow any fresh air into the house. Since then I have been leaving windows open and getting house air circulation which has helped alot.
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.