Allow 10% runoff. Collect it and check the Ph and PPM. The range it should be is 5.8-7. 6.5 is optimal at your stage. 6.0 is optimal for best root growth and good for veg. Targeting more P and K in the upper ranges of Ph and all nutrients available at 6.5.
It will take you 2 watering to diagnose any issues. Feeding exactly the same both times with 10% runoff. So feed with the nutrients you always do and no water only or anything. Same PPM feed each time.
If PPM rises sharply, lockout has occurred. Reduce to 1/4 normal feed and allow 10% runoff to test and record every feed. You can go back to normal PPM feed when your numbers drop to a more comfortable level. You will have also diluted and allowed the roots to use some of those nutrients that were locked up will be available and allow her to “unclog”. So when you go back to regular feed, she invites it with open arms.
If Ph is off, you can use top dressings. If using synthetic like Ph down, you can simply counter it by using a lower feed water Ph. Using Ph down all the time is not desirable. But if you must use it to keep her eating properly and do not plan to make major adjustments, do it and force her to be in range if it means she eats correctly. If close to harvest window, sometimes it is the best to not care too much if your forcing her Ph with synthetics if it means she stays healthy. But it means you are not feeding her correctly with proper Ph or the medium buffering is less effective that late.
Ph swings or rises typically stem from soil temperatures having a swing upon feeding or cooling of the medium. So pay attention to your soil temperatures AND your feed water temperatures. Your 66 degree feed water may say 6.5 Ph, but your soil temp is 70 degrees, you’ll cool the medium upon feeding and then the medium temps will rise to its normal. That increase in temperature will increase the medium Ph. So Ph can be wonky as it does naturally swings with these temperature changes and that’s ok, that’s why it isn’t advisable to Ph down/up chasing small, in range swings.
You should always 10% runout and record runoff numbers Ph and PPM, to monitor root health. Soil growers have no other means to know their root zone unless they runoff check. Hydro does the same but can spot minor fluctuations as Ph and PPM of the water can be checked daily.