Backyard Aquaponics
A place to discuss aquaponics

I've read multiple threads about how gravel has raised the ph of AP system and so I decided to test from my local gravel pit before I bought and I'm getting a lower ph reading than before I added the rock. Here's what I did:

I got two cups from my kitchen and put my very well cleaned sample, about a handful, in one cup and filled them both about 3/4 with distilled water from the same jug. After about 14 hours I put my Hannah ph meter in the one with just distilled water and got a reading of about 7.5 and the cup with the gravel read about 6.8.

So my question is after reading threads of mediums raising ph is it possible my local gravel is lowering the it instead or have I done something wrong? I need to figure this out soon as I'm almost ready to add medium to my AP build.

Yes, it's possible, it just depends on the composition of the rock. Most rock works fine but limestone buffers the pH up too high. We usually aren't that concerned about the rest because they aren't a problem.