After hearing about PH changes I jumped.
I brought home a PH meter from work and tested my water.
500 Gal with a 5.4 PH at the start.
I also got from work Caustic potash flakes.
I added SMALL amount 6 - 8 flakes and took two tests.
I average 7.5 & 7.1 as water cycled through the pond.

That with my barley straw I hope to see less bottom grass soon.

Rich