Maybe put a powerhead in the qt and point it upwards a bit, might bring the ph up a bit. Also, when did you test the ph? It will be lowest after the lights are out for awhile and then in the morning it will start to rise.
7.8 is not great but it isnt bad. you dont wanna start dosing chemicals now, it will just mess with the whole situation and your fish are sick already. If it drops lower I'd say do a decent water change to get it up as most salt mixes will bring it to where it needs to be
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.