Ph question

Sounds to me like the same issue I'm dealing with currently. After I adjust my tap water ph it goes back up over time just like u. Mite be super high Alkalinity in ur tap water. Basically the water has some minerals that keeps it at around 9 for me no matter what I do. so the solution I'm told is RO system and then adding back 10-15% of tap water and that keep it stable at around 6.8. Get a home water test and test your water to figure out what your problem is. "Water alkalinity and pH are not the same. Water pH measures the amount of hydrogen (acid ions) in the water, whereas water alkalinity is a measure of the carbonate and bicarbonate levels in water. Think of carbonates and bicarbonates as dissolved limestone." Natural pH buffers would be something like peat moss in your soil I haven't tried this yet in growing but I know it works in aquariums to stabilize and lower pH. I'm basically on a hunt to figure out what to do myself keep in touch.