Low pH level

What is the DKH running and Magnesium ? CO2 is a acidic gas and Ph in and of its self means little other then a measurement to tel if there is sufficient amounts of carbonates in the system to off set acids . Now the tops caused the interference with the surface exchange of the CO2 gas for Oxygen gas . But if you have enough Carbonates in solution then there should be no problem with the Ph jumping back up and adding a bunch of baking soda is not a good idea as the salts then to pull Ph down . Get a good DKH test kit and a good reef buffer or make your own and get the DKH up and forget about Ph .

I think you must also be testing Ph with a test kit and if you had a ph of 7.4 or 7.5 then nothing much would be alive in the tank.. Unless you have a monitor and calibrate it regularly then you have no clue as to what the Ph really is at any given time of day.. Early AM before lights is the lowest point and just before lights out at days end is the highest point of a Ph reading

Testing a marine reef tanks Ph using a test kit is a waste of test kit money and time that would be better spent on the DKH levels if you rally want to keep the Ph up and regulated ..

 

pH fluctuates through the day. The net consumption of carbon dioxide during the daylight hours, leads to some aquariums to become deficient in CO2 during the day, and the pH rises.If you are having dramatic fluctuations you can aerate the aquarium water to degass excess carbon dioxide. Also try using a salt mix with a naturally higher buffering capacity like Tropic Marin or add buffer to raise your alkalinity to help reduced the pH swings