the problem is not a yo-yo effect.
here are 2 test that were run 10 mins apart.
#1 i ran the test on the left: ph and high range ph.
#2 then added ammonia
#3 ran test on the right: ph and high range ph.
appears that the ammonia messed up the ph test.
i am willing to bet once i no longer have to add ammonia my ph problem will go away.
just never heard of ammonia altering the ph results.
with my current tap ph of 7.4-8.0 i should be ok. my platy tank never had any issues.
the 75g will be a schooling tank, tetras, rainbow fish, and cories.
in a perfect world i would like a ph of 7.0, but i know that probably wont happen with my water.
i thought of adding peat or driftwood, but water changes might cause too much of a swing.