Backyard Aquaponics
A place to discuss aquaponics

My system has been running for a few years now but the pH still refuses to go down. I have tried replacing the media twice, doing repeated frequent water changes, adding vinegar regularly, using a brita water filter on my tap, using chemical pH adjusters, adding more plants and fish, and using distilled water exclusively. All of these attempts were tried for months at a time, but none of them brought it down below 7.8 and it just went right back up to 8.2 within a week, where it sits at all other times that I test it. I am completely out of ideas and endlessly perplexed and frustrated as to why it is still not going down. I have tried researching the issue but the only advice I can find seems to be about buffering it up, the opposite of what I need. I am open to any ideas and suggestions.

There are countless threads on this forum about this topic.

Search for hydrochloric acid or muriatic acid (same thing). Use it to treat top up water then add that to the system.

Have you done the vinegar test on your media?

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If it's not your source water or media, you might have denitrification going on in your system. Denitrification is caused by anaerobic zones, and it leads to an increase in pH. What are your ammonia and nitrate levels, what is your stocking density like, and how many plants do you have in it currently?

Edit: A side note, I like to use 85% food grade phosphoric acid as an acidifying agent. It is a triprotic acid, and its ability to donate multiple protons seems to make it more effective at neutralizing alkaline buffer systems in the water than monoprotic and diprotic acids. Plus, it adds phosphate to your system. Whatever you decide to use as your acidifying agent, avoid anything containing citric or acetic acid since they are antimicrobial agents that can damage your colonies of nitrifiers. I have gotten ammonia issues from using products containing citric acid in the past.