i grow the same way, if your ph is over 7.5 or lower than 5.5, your plant wont be able to absorb the nutes, when my ph gets too high, i use 2 tablespoons of distilled white vinegar, yes i said distilled white vinegar.
it seems weird but it keeps my ph down to 5.5 to 6.5
and i use baking soda to raise my ph, but that`s not a problem with the water i use
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hope this helps
sorry, that`s 2 tablespoons per gallon of water used
and remember to use ph balanced water ONLY in the last week or two of flowering to get rid of that chemical taste your bud will have if you dont.