flushing?

I just noticed some yellowing tips on my ladies. I'm using all the same techniques and nutrients that have worked for years. My tap water always comes out high 7.0-8.0 after adding nutes (Nova) it drops to low 6's. But I just checked my nutrient solution and its low 5's. My question is should I wait until they are thirsty to flush and correct or start to flush before they really need water? Thanks for any input.

Frankly I would do neither, I would consider repotting. You don't say you are at the end of your growth cycle, so I am assuming. Might be nute lockout, usually corrects for me with repotting.....but I give little in the nutes dept.

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-shake