I need some advice on my aquaponics system. I have a 900 gallon system w/tilapia fingerlings and lava rock in my growbeds. The tilapia are doing great but my pH is really high. I have hard water and my pH is 8.2 (not very good for plants to thrive). Do you have any suggestions for lowering my pH where I don't always have to add pH down. I really don't want to have to add "chemicals" every day or when I have to top my totes off. Any suggestions would be awesome. My system has been cycling for about 3 weeks now and the pH is still very high.
I'm just beginning in to experiment with AP, but here is my $0.02
Avoid HCl. HCl is what you use to both lower pH and chlorinate your pool!
You are adding a toxic element to your aquaculture. I have been using phosphoric acid and it works great and since it is triprotic (releases 3 hydrogen ions) it has 3 pKa's and is milder than HCl and is a sort of buffer as well. Also, it adds a bit of P, which is a plant macronutrient. You can get it in bulk in either solid or concentrated form. I am only running 50 gallons, but only use about 10 drops to get my pH from 8 to 7, for example. So the quart I purchased should last me forever.
I know I'm not addressing the chronic nature of your high pH. There are other things you will have to use to address that or I suppose you could put your system on some sort of phosphoric drip.
At any rate, I would ditch the HCl. You don't want the chlorine. As your system matures, you may find the pH will come down.
Sorry, just realized there are tons of replies here and some give the same advice . . .