Star flushing the soil, water ph 5,6, but runoff p...

Flushing is not need unless you're correcting an catastrophic issue in the medium. If you doing this for end of life, its wasted effort. IMO, others will have their own views. To many other details missing to solve the issue. It could be likely their is a good amount of buffing agents in your medium and that's why PH is coming out higher then desired. Or you pen needs calibration. or the PH is not stable and is drifting. try adjusting your water and letting it sit out with PH down in for 24-48 hrs. then test it again. is it the same PH? if not then its drifting. and if its drifting up, then that means its getting used up. end of day, do plants look healthy? if yes = don't fix whats not broken.