No expert here either, but I will concur that your PH is too low. It should be 8.2-8.4. A water change should help. If you keep having PH problems it could be due to low alkalinity, in which case a buffer needs to be added to increase the alkalinity. This will in turn keep your PH stable. HTH
No expert here either, but I'd check into your alkalinity. Looking for 3-4 range with 3.5 ideal. This will help buffer your water. If your alkalinity is fine then you need to raise you ph. Good water change the best way. Let us know your alk reading.