I'm only 12 months into my AP journey so you might want to search the website and wait for others to chime in but I'll hazard a guess that once your system matures a little then the pH will come down naturally. I'm guessing you're still in the cycling phase > have you been testing your water chemistry?
Patience....
I can tell you this from my own experience, I tested my large outdoor system (1000-1200L water/300L grow media)regularly and the pH didn't drop for approx. 4 months. Then I got a bit slack in testing it (pH) because it had been so stable. I had a fish die so I checked the pH and it had dropped right down.
From what I understand, the pH will drop by itself as the nitrification process happens and then you'll be regularly adjusting the ph to raise it.
I'm now adding a tablespoon of hydrated lime once or twice a week (1000-1200litres) of water to raise the pH to 6.2-6.8 as well as the occasional dash of potash and magnesium sulphate.
I don't really know for sure, but I don't think a slightly high pH will be all that bad for the fish or the plants however if I'm wrong on any of my info then I'd suggest you post pics of your system/water tests for others to review.
I'd still think that your system is very new, won't have finished cycling and in about 4-6months time (pending on the pH of your water source for top ups) you'll be raising the pH like most seem to have to do.
I could be missing something but with such a new system, just give it some time mate!
and keep on top of the water tests (daily) for the first 6weeks, then once it's completed cycling you can probably just test once a week and watch for the point the water pH drops dramatically