pH swings and airstones - my observation

For months I've been plagued with pH swings in my reservoir.

I'll leave the tank overnight and come back to a 7.8 pH. I'll pour in some pH Down to 5.8 and come back a few hours later and it's crawled back up to 7+

I'm using tapwater with H&G coco a+b, multizyme, nitrogen, roots excelurator, bud xl, top shooter, Mammoth p and Great White in a DTW system with coco. Over the months I've added and removed all sorts of things to try fix this issue but keep hitting the same problem

I got one of the bluelight PH adjuster modules and over 2 days it pumped a whole 500mL bottle of pH down into the res

Obviously not ideal

Finally after some reading inline I found some posts from people suggesting the airstones may be causing the pH swings followed by heaps of posts by people saying the suggestion was impossible and stupid and they'd never had problems with airstones

Anyway after months of adjusting every other variable today I decided to try removing the airstones and what do you know all of a sudden my pH sits and stays at 5.8 with barely a decimal of swing over the whole day.

Thoughts?

I noticed the exact same thing because I get tired of phing last minute and I like stable reading before using. I have a flat 6 inch in bottom and another round one about 4 or 5 " long. I believe the oxygen is evaporating the ph serum.

i dont have a res but i fill up 5 gallon buckets with airstones. with my research the ph rises cause the amount of oxygen is being introduce to the water.