Run-off low - Nutrient lockout

[DontEvenAsk]

Had a slight nutrient lockout issue. The older leaves were looking a bit yellow, some signs of magnesium deficiency too, but the newer leaves are looking green and happy, besides a select few. Here's the run down.

Medium: 6" Rockwool Blocks
Phase: Flowering
PH going in: 5.8
PH going out (runoff): 4.8
PPMs: ~1300

MY Solution: I flushed each Rockwool 3 times using PURE RO water PH'ed to 5.9-6.0, but the run off for some of them is still coming out low, around 4.8-5.2.

What do you guys suggest? Should I flush with an even higher PH'd RO water next time to balance it? Say, 6.5? Would that bring my rootzone back to 5.5+? Any suggestions appreciated.

 

[Scientific]

That's some pretty magical rock wool that can drop the pH of a nutrient solution by 1.0. That doesn't seem to make sense.

Some thoughts/questions just to maybe prime the troubleshooting process:

• How are you measuring pH? If with a pH pen, have you calibrated it in pH 7.0 solution?
• I've gotta say, wow, at 1300 PPM, that's some really concentrated fertilizer you're using there...
• When you adjust the pH of your nute solution, are you letting it sit for an hour to let the pH stabilize? I'd suggest trying that. Trying to explain why your pH is shifting, I'm wondering if somehow the buffers in the nute solution aren't changing the pH (though I would guess that they would drive it the other way--higher).

A couple more thoughts:

Don't be too quick to say "I have nutrient lock out" or "I have an X deficiency." It's usually more complicated than that.

It's hard to lock out nutrients with modern fertilizers since they are formulated to work over a broad range of pHs, and making a diagnosis from a leaf chart is difficult and error-prone. Rather than saying, "I have this problem," it's usually better to think in terms of "This is a possible explanation."

I hope that's not too pedantic. Just my .02. Good luck.

 

[DontEvenAsk]

That's some pretty magical rock wool that can drop the pH of a nutrient solution by 1.0. That doesn't seem to make sense.

Some thoughts/questions just to maybe prime the troubleshooting process:

• How are you measuring pH? If with a pH pen, have you calibrated it in pH 7.0 solution?
• I've gotta say, wow, at 1300 PPM, that's some really concentrated fertilizer you're using there...
• When you adjust the pH of your nute solution, are you letting it sit for an hour to let the pH stabilize? I'd suggest trying that. Trying to explain why your pH is shifting, I'm wondering if somehow the buffers in the nute solution aren't changing the pH (though I would guess that they would drive it the other way--higher).

A couple more thoughts:

Don't be too quick to say "I have nutrient lock out" or "I have an X deficiency." It's usually more complicated than that.

It's hard to lock out nutrients with modern fertilizers since they are formulated to work over a broad range of pHs, and making a diagnosis from a leaf chart is difficult and error-prone. Rather than saying, "I have this problem," it's usually better to think in terms of "This is a possible explanation."

I hope that's not too pedantic. Just my .02. Good luck.

I appreciate the .02. Anything helps.

1. How are you measuring pH? - I'm using the bluelab combo meter, but I calibrate the pH meter weekly so I'm 99.99% sure it's not the meter messing up.

2. When you adjust the pH of your nute solution, are you letting it sit for an hour to let the pH stabilize? - Yep, I always mix my nutrients and adjust PH 30 minutes to 1 hour before the feeding timer comes on. Should I wait longer..?

Just looking for any possible solutions to adjust the run-off back to normal. So I don't have to feed pure RO water at 6.0 and have the run-off come back at 4.8 again!

 

[Scientific]

I appreciate the .02. Anything helps.

1. How are you measuring pH? - I'm using the bluelab combo meter, but I calibrate the pH meter weekly so I'm 99.99% sure it's not the meter messing up.

2. When you adjust the pH of your nute solution, are you letting it sit for an hour to let the pH stabilize? - Yep, I always mix my nutrients and adjust PH 30 minutes to 1 hour before the feeding timer comes on. Should I wait longer..?

Just looking for any possible solutions to adjust the run-off back to normal. So I don't have to feed pure RO water at 6.0 and have the run-off come back at 4.8 again!

You have a much better pH meter than I do!

OK then, I'm out of ideas. We'll have to go with magic rock wool! (What's weird is that rock wool has a reputation for raising pH. )

 

[Cultivator]

Never flush with plain water, especially ro water to try and rectify a problem, its likely to make it worse. When ever you flush in hydro, apart from final flush, always flush with a basic nutrient mix that os pb adjusted. Tbis will do 2 things. First it will clean out excess salts, think of it like bluetac, the easiest way to remove excess blutac is to take a ball of it and dab it on the little bits, it will pick the little pieces up leaving the area clean. Secondly it will keeo the medium conditioned to growth, you need to keep nutrient in hydroponic medium sonthe plants have access to it.

What are your roots looking like? Thr 2 biggest cause of probs in rockwool are ph out of balance and/or root issues such as root rot from over saturation of the media which is def possible in rockwool although unlikely at half way point of flower. Warm water also causes root rot. Root problems always show as deficiencies in the leaves..

Dont worry about your run off so much. Your run off can have high ec and low/high ph and thats quite normal in hydro. Plants use differnet elements at different time and the run off shouldnt be what is going in because then it means tbe plant is using nothing. I never check run off as its not necessary. Focus on what you are putting in is correct. 1300ppm is fine for rockwool, you could go as high as 1450ppm comfortably if plants are large and healthy.

What is your nutrient mix? Exactly?