Potassium Deficiency or Overwatering?

Ppfd 700 on a veg schedule is too much light, you’re not running 12/12 right? If you’re running like 18 hours at 700 canopy level it’s too much and it’ll make whatever is causing your issue worse.

nxsov180db said:

Ppfd 700 on a veg schedule is too much light, you’re not running 12/12 right? If you’re running like 18 hours at 700 canopy level it’s too much and it’ll make whatever is causing your issue worse.

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I'm on 18/6. I've been following Jorge Cervantes grow bible...I think he recommends 700 after 4/5 weeks in veg. What would you recommend?

jimbonorman said:

I'm on 18/6. I've been following Jorge Cervantes grow bible...I think he recommends 700 after 4/5 weeks in veg. What would you recommend?

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This is assuming all of the other variables are running perfectly ( nutes, air, water,temp, etc)

jimbonorman said:

I'm on 18/6. I've been following Jorge Cervantes grow bible...I think he recommends 700 after 4/5 weeks in veg. What would you recommend?

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400-500 unless they’re vigorous with co2 and a high ec to support the light.

nxsov180db said:

400-500 unless they’re vigorous with co2 and a high ec to support the light.

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Ok well they were actually around 680 so I dropped them to 600. Curious what others think about this. You can see from pics this morning they seem to be praying/enjoying the light? At least I don’t see any burn or canoeing on the newest growth, but please correct me if you see otherwise.

The one thing that has me wondering about the light is this one branch that’s been in the shade the whole time (I’ve circled this in the third pic). Does this indicate that my main problem could actually be light burn and nothing else? Or is the core issue being exacerbated by light?

Way too much light. 400-500ppfd is the right spot.

pegboy said:

Way too much light. 400-500ppfd is the right spot.

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Done. Thank you!

So does anyone here ever push it to 700 without CO2?

jimbonorman said:

Done. Thank you!

So does anyone here ever push it to 700 without CO2?

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Have you checked your ph or recalibrated your yellow ph meter yet? The light didn't cause those yellow leaf edges.

jimbonorman said:

Done. Thank you!

So does anyone here ever push it to 700 without CO2?

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That amount of light without co2 may certainly be possible, I've never tried it or felt the need to, 400-500 works for me and if I want to speed things up I run 24/0 instead of 18/6 which is similar but a little less to the DLI of 700 at 18/6. Another thing to keep in mind is if your plants are struggling they won't be able to handle as much light, intense light is only for plants that are thriving.

Cousin Bo said:

Have you checked your ph or recalibrated your yellow ph meter yet? The light didn't cause those yellow leaf edges.

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Not yet. I watered them yesterday morning so I have to wait until Fri or Sat to soak them and check runoff. I did check the soil ph with the 3-in-1 ph/moisture/light meter and it clocked in between 7 and 8. Not sure how accurate the meter is, though, as it was also a $10 special.

I ordered the Apera meter yesterday - should be here tomorrow so I’ll first compare the tap water reading between that and the yellow meter to see how badly the Vivosun meter has drifted. Then I’ll obviously use the Apera for the next watering.

The fun continues - stay tuned…

nxsov180db said:

That amount of light without co2 may certainly be possible, I've never tried it or felt the need to, 400-500 works for me and if I want to speed things up I run 24/0 instead of 18/6 which is similar but a little less to the DLI of 700 at 18/6. Another thing to keep in mind is if your plants are struggling they won't be able to handle as much light, intense light is only for plants that are thriving.

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Yeah I think this is what’s behind that one branch that looks unblemished in the shade. PH is likely off and intense light has exacerbated (dare I say illuminated) the issue. Dialed it back to 450 PPFD until I can stabilize her…then I’ll prob start slowly increasing it again and screw something else up

jimbonorman said:

Not yet. I watered them yesterday morning so I have to wait until Fri or Sat to soak them and check runoff. I did check the soil ph with the 3-in-1 ph/moisture/light meter and it clocked in between 7 and 8. Not sure how accurate the meter is, though, as it was also a $10 special.

I ordered the Apera meter yesterday - should be here tomorrow so I’ll first compare the tap water reading between that and the yellow meter to see how badly the Vivosun meter has drifted. Then I’ll obviously use the Apera for the next watering.

The fun continues - stay tuned…

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Congrats on the Apera. You can go ahead and toss that 3 in 1 thing in the trash, lol. Those things suck. You don't really need to wait to check them as long as you have a reliable way to test the ph. The pots don't really have to dry out between watering every time. If it was me I'd test it now and if the soil ph is as low as we think it might be I'd start correcting now with higher ph water like tstick was saying. My guess is the yellow meter is showing a higher ph than it actually is. Just a guess but it would explain those damaged leaves.

Cousin Bo said:

Congrats on the Apera. You can go ahead and toss that 3 in 1 thing in the trash, lol. Those things suck. You don't really need to wait to check them as long as you have a reliable way to test the ph. The pots don't really have to dry out between watering every time. If it was me I'd test it now and if the soil ph is as low as we think it might be I'd start correcting now with higher ph water like tstick was saying. My guess is the yellow meter is showing a higher ph than it actually is. Just a guess but it would explain those damaged leaves.

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lol I suspected the meter might be junk.

I would agree and I'm assuming the Vivosun meter was reading higher. If I can pick up some distilled water today and recalibrate the Vivosun then I'll go ahead with the test, otherwise it will have to wait until tomorrow when I get the Apera.

jimbonorman said:

lol I suspected the meter might be junk.

I would agree and I'm assuming the Vivosun meter was reading higher. If I can pick up some distilled water today and recalibrate the Vivosun then I'll go ahead with the test, otherwise it will have to wait until tomorrow when I get the Apera.

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If you have a Walmart of pet store around you could get a ph test kit for an aquarium. It's the same thing as the ones in hydro shops. But if you're getting the Apera tomorrow that works too.

Cousin Bo said:

If you have a Walmart of pet store around you could get a ph test kit for an aquarium. It's the same thing as the ones in hydro shops. But if you're getting the Apera tomorrow that works too.

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OK I think it’s the dirt.

The Apera isn’t coming until later tonight so I went ahead and calibrated the Vivosun ph meter with distilled water and discovered it was drifting 0.5 lower…which means when I thought I was at 6.5 I was really at 7…which better than being 6, I guess. Tap water comes out at 9.3, not 8.8

I then gave them some water at 6.5 and the runoff was roughly 5.5. Should the run-off ph match the input ph? If yes, then I think I found the problem. Next question is what can I do about it?

I’ve got some dolomite lime in the garage…thinking I should drop maybe 5 tbsp into each 5 gal pot…only problem is I can’t evenly mix it around so it will sit at the top…

jimbonorman said:

OK I think it’s the dirt.

The Apera isn’t coming until later tonight so I went ahead and calibrated the Vivosun ph meter with distilled water and discovered it was drifting 0.5 lower…which means when I thought I was at 6.5 I was really at 7…which better than being 6, I guess. Tap water comes out at 9.3, not 8.8

I then gave them some water at 6.5 and the runoff was roughly 5.5. Should the run-off ph match the input ph? If yes, then I think I found the problem. Next question is what can I do about it?

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You cannot calibrate a pH meter with distilled water!
Until you can calibrate it properly, your readings are meaningless.

Billy the Mountain said:

You cannot calibrate a pH meter with distilled water!
Until you can calibrate it properly, your readings are meaningless.

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All the instructions online say to use distilled water - what is the proper way to calibrate the ph meter?

jimbonorman said:

All the instructions online say to use distilled water - what is the proper way to calibrate the ph meter?

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If you've genuinely seen instructions to calibrate a pH meter in distilled water, please post them.

Distilled water has no free H+ and OH- ions to be measured by a pH meter. Since H+ = OH- (0=0) it's pH is seven by definition, not measurement.

To correctly calibrate your pH meter, you need pH calibration fluid, not distilled water.

Billy the Mountain said:

If you've genuinely seen instructions to calibrate a pH meter in distilled water, please post them.

Distilled water has no free H+ and OH- ions to be measured by a pH meter. Since H+ = OH- (0=0) it's pH is seven by definition, not measurement.

To correctly calibrate your pH meter, you need pH calibration fluid, not distilled water.

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I have not scoured the web for too many instructions, but all that I came across advised to use distilled water. Here are a few:

Instructions 1
Instructions 2
Instructions 3
Instructions 4

I used the provided packets that dissolve into water in order to calibrate the meter, FYI.