2 - I strongly recommend more waterflow. An appropriately sized powerhead will do the trick. More waterflow will improve gas exchange and remove more CO2 from the water. Excess dissolved CO2 will lower PH.
3 - adding #2 can counteract the negatives of having a cover. A skimmer would be even better. A cover lowers gas exchange and this can cause excess CO2 in the water. Excess dissolved CO2 will lower PH.
4 - Detritus is biological waste. It can be anything from dead algae pieces to fish poop. Decaying organic matter releases metabolic acids that can lower PH.
6 - Alkalinity is a very important component of a healthy saltwater system. I recomment you get a test kit and try to maintain Alkalinity near 3.5 Meq/L. Low Alkalinity can cause an unstable PH, usually on the low side.
7 - 1.022 is a Specific Gravity reading. I would also need the water temperature to convert this to Salinity. Salinity should be between 35ppt and 37ppt if you are keeping invertebrates (Corals, Shrimp, Starfish, etc.). That would be a Specific Gravity reading of about 1.025 when the water temp is 80F. Raising your Salinity should also help your PH but only slightly.
