PH changes over the daily cycle. You need to measure alkalinity. You can try to take pH several times over the day early am . noon and dark and compare to see the change. Ag lime will help increase alkalinity. Alkalinity buffers pH swings. I am assuming this is a soil bottom pond.

See charts in this archive link.

http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=96127#Post96127

Last edited by ewest; 07/01/19 10:01 AM.