I used to have some bad problems with ph fluctuating, it still rises a little but is much more manageable.
This is my routine for nutes.
When I am due a nute changeover, 3 days before I fill up my spare tote with tap water (I am in Scotland so the ph is 6.8-7.2 and ec is 0.1)
I leave the lid off for 48 hours to allow for chlorine to dissapate.
I then add my nutes and ph to 5.5.
This then sits for 24 hours(Thanks THG)
Then I recheck the ph and adjust as needed.
Only then are my plants allowed near it.
The water replacing the water the plants take from the solution (top ups) also sits out and is ph'd for 24 hours before letting it near my plants, I am quite paranoid about it.
By following this regime, I find I dont have to ph the solutions the plants are in any more. I check it daily, but never need to adjust. I use AN nutes which have some kind of ph guarantee.
One thing to remember is that as the plants drink, they take out water but leave the nutes behind, meaning your level will drop, so will your ph, while you ec will rise.
I would recommend leaving the ph alone for a few days, monitor it so it doesnt go mad high, but leave it to allow the buffers in the nutes to work. I was the same way early on but now I just concentrate on what I am adding to my grow and that takes care of the grow.
Green mojo fella.
W