Shelly wrote:

I have a small pond (~400 gal) and I have a Ph problem. The Ph of the
city water here is 7.4 but after a few days in my pond the Ph goes to
8.0. I'm not sure why, my guess is maybe there's a rock in there that's
elevating the Ph. I feed my fish tons of food and I have it a "little"
bit over-stocked which you'd think would lower the Ph, and then after a
few days it's back up to 8.0. Should I leave it alone or should I put
some peat in the filter system?

That is a very small change, and a not bad at all pH.

I'd suggest leaving it alone.