Quote Originally Posted by Rusty Trichome
Runoff ph indicates the interraction between soil ph and water ph, and yes...it is an invaluable indicator. Nutrient uptake is limited on the outside edges of our ph. Lockouts will occur.

Are you adjusting the water before adding the nutrients? Every nutrient I've ever worked with is acidic (FF included) to some extent, and will lower your ph.
Well, the plants that had the problem have only had nutrients once. And I mix the nutrients and then later adjust the pH, however, I probably won't even adjust pH anymore. Tap water is at about 7.8 and after nutes it can come down to 7.1 or so. Just a 1/4 tsp of pH down per 5gal will get it at 6.9-7.0. I'm watering on the high-end of the range or neutral...

What I meant was Humboldt Nutrients doesn't lower it that much... not as much as I expected. It can lower about 0.2 - 0.7 pH so far from what I've seen depending on the nute combo used and the concentration at which it's mixed.

I agree that runoff pH is helpful.. but I think the pH is probably different at any given location in the pot... so even though it may be at 5.0 when it comes out of the pot... all hope may not be lost