m0useanswered grow question 3 years ago When in doubt flush them out with more solution till you get your desired PH.
Your in hydro and this is a nice and easy way to fix it.
Coco also tends to do this, buffer build up.
I would flush with PH'd water and a week solution of calmg 1ml/l
Will help fix any cation exchange sites that may have opened up as its degrades throughout the grow.
Follow though with your scheduled nutrients when you hit your PH mark.
Good Luck!