Here's the thing about pH. It's stubborn. It sits where it sits in your tank for a reason. The environmental acids in your tank (from CO2, NHx, fish droppings, etc) all contribute to drive it lower than natural reefs. This can't be helped much, other than more regular water changes, bigass skimmers, fresh air feeds, etc. The problem is compounded by inaccurate measuring. Most probes, unless freshly cleaned and calibrated, are going to give false readings. Titration kits get thrown off as soon as you move the water into the testing vial.
Now the next thing that happens, the hobbyist freaks out at the 7.9 reading and tries to chemically adjust. But the tank is happy where it is, and tries to stay there. Yup, more chemicals
This becomes a cycle of insanity with the tank (water) generally winning. The tank inhabitants often suffer a bit more. Sometimes a lot more.
If your tank says 7.8, or 8.4, or whatever, and there is no glaring problem with the tank, leave it alone. You'll likely do more harm than good, trying to fix a problem that doesn't exist. As for PO4 leaching because the pH "says" it's a bit lower than a natural reef, not gonna happen. If the PO4 is leaching, you just have too much in the tank. It's not a pH thing.
IMO, pH is the last thing a hobbyist should test for. I know some people like to test, so test for NO3 instead. If you have some, it's much easier to fix, and will give you results you can see.