Unstoppable mag deficiency under LED

[dirty budster]

I have been fighting this mag deficiency for nearly two weeks and I haven't made a lot of progress so I figured I would post in here and see if anyone have some hints what could be wrong.
I started a journal on here, see below, but I will make a short summary in this thread.

https://www.autoflower.org/f52/cbd-kush-blueberry-scrog-under-gn-rebel-32625.html

SETUP

Tent: 60x60x120cm (2x2x4 ft) Homebox XS
Fan: TD silent 280/380m3/h running at 150V
Filter: Carbon active 300m3/h
Light: GN MS0006 with 6 rebel modules.
Soil: Plagron grow-mix in 6.5L square pots + 2 tbsp of dolomite lime per pot and ~30% perlite
Nutrients: Canna rhizotonic root stimulator, TNT complex(veg), bloom complex and phosphorus plus
SCROG net with 5cm squares
Seeds: 3xDP CBD Kush and 1xDP Blueberry

Day 1 I started the plants under 2 rebel modules 50 cm away.

Day 9-10 I noticed the mag deficiency on the second set of leaves on one of the plants. I realized that the light was probably too close so I raised it to 70cm and started foliar feeding with rhizotonic and cal-mag twice daily. The pots were drying out so I gave them 0.25l of water with rhizotonic.

Day 13 New growth was looking healthier so I thougt I might be out of the woods.

Day 15 I noticed mag def on the new growth as well.

Day 17 The pots had dried out a bit more so I gave them their first feeding with rhizotonic, 1/5 grow nutes and a full dose of cal-mag at pH6.5. I gave each plant 0.5l. I switched to foliar feeding with epsom salts and rhizo twice daily as the cal-mag didn't seem to work that well as a foliar feed.

Day 19 New growth was looking better again.

Day 21 I guess you can see where this is going by now but the new growth started showing signs of mag def again. Since the soil was still quite moist I didn't want to give them too much water so I prepared 0.25l per plant. I mixed rhizotonic with a double dose of cal-mag and 2/5 of veg nutes.

Day 22 Today. I did a slurry test of the soil and the pH came out to 6.8, a bit high, probably due to the dolomite lime, but I wouldn't expect massive issues because of it.

Now onto the pictures

Day 9

Day 10

The leaves where I first spotted the problem.

Day 15

Pretty clear mag def on all plants

Day 19

Day 22

That's it, if anyone has any ideas or if you see something I did wrong I would be happy to hear it. Also, if anyone has some hints on how to avoid this in future grows that would be appreciated as well. I'm considering going back to CFL for the first couple of weeks as I never had much issues with that. This turned out to be a bit longer than I expected so thanks to everyone who managed to plow through it

 

[Trapper]

at 6.8 the mag should be readily available via the roots...

BTW, other than the light ting...they look absolutely beautiful

 

[GCase]

Just a quick comment to subscribe.

Soil has lots of goodies. Some may not be available until broke down. Just wonder if it is an N issue. See just a few minor rusty colored spots on a few leaves.

If mag--a quick fix is to use a liquid--cal/mag which also has a bit of N (usually).

Standing by to see what others have to say. Otherwise, plants look healthy.

_______________________

Right Stick on the uptake--both N and mag--and in both soil and soiless have a broad alkaline range. Could be needs a shot of N and no harm in using cal/mag.

 

[dazedandconfuzed]

Hi Dirty B, I'm interested to see how this works out for you. Lime seemed to make mine a little better, I keep having issues too. Karma hope it works out for you bro.

Peace,

Dazed..

 

[dirty budster]

at 6.8 the mag should be readily available via the roots...

BTW, other than the light ting...they look absolutely beautiful

Thanks man! They don't look too bad but they're also not as healthy as they could be. I had even worse mag issues last grow and it really hurt the yield in the end. I'm glad I'm doing photos this time as I can let them go a bit longer in veg to compensate.

Just a quick comment to subscribe.

Soil has lots of goodies. Some may not be available until broke down. Just wonder if it is an N issue. See just a few minor rusty colored spots on a few leaves.

If mag--a quick fix is to use a liquid--cal/mag which also has a bit of N (usually).

Standing by to see what others have to say. Otherwise, plants look healthy.

_______________________

Right Stick on the uptake--both N and mag--and in both soil and soiless have a broad alkaline range. Could be needs a shot of N and no harm in using cal/mag.

I have been using Botanicare cal-mag plus, which contains 2% N as well. I also gave them a small amount of veg nutes and in addition the rhizotonic contains a small amount of N as well. But you're right it looks like they could use more N.

Hi Dirty B, I'm interested to see how this works out for you. Lime seemed to make mine a little better, I keep having issues too. Karma hope it works out for you bro.

Peace,

Dazed..

Since I had issues last grow I added the dolomite lime this time but it doesn't seem to be enough. I prepared the soil 4 weeks in advance so I thought that would have been enough time for the lime to be useful. Thanks for the karma!

 

[namvet25]

I also think it is nitrogen def because the entire plant is light green.You need some nutes with higer nit count.

 

[oldster]

Hi DB,

If your water is going in at 6.5 and runoff is 6.8 your soil pH would be 7.1. Have you calibrated your pH meter recently? If it is reading low with already high soil pH it could put you in the lockout range

 

[dirty budster]

Hi DB,

If your water is going in at 6.5 and runoff is 6.8 your soil pH would be 7.1. Have you calibrated your pH meter recently? If it is reading low with already high soil pH it could put you in the lockout range

I checked the calibration of the pH meter recently. I didn't measure the run-off I mixed some soil with water and measured the pH of the slurry. That should show the pH of the soil.

Thanks for the inputs guys. I gave them 0.5l each with a full dose of veg nutes and a double dose of cal-mag. I would have given them more but the soil was still quite moist and I didn't want to overwater them, The new growth is looking greener but after a few days I can still see signs of mag def although less severe than before. I'm gonna wait a few more days until the pots have dried out before feeding them again. This time they will be getting a proper watering until run-off. They ususally take slightly less than 2l when dry so the question is how much nutes to give them?
I will definitely give them a double dose of cal-mag as it seems they can't get enough of it. For the base nutes I'm thinking a full dose of veg nutes again. I'm a bit concerned about burning them since the total amount of nutes will be larger compared to only giving them 0.5l. When watering with smaller amounts I imagine the nutes get diluted in the soil to some extent.

Here they are on day 29

All together

CBD 1

 

[dazedandconfuzed]

Really hope this gets better for you bro. It's like I'm looking at my grows all over again....
I wish I could be of more help, figure it out for the both of us!

 

[dirty budster]

Thanks dazed, I hope so too. I'm hoping letting them go a bit longer in veg will be enough for them to recover.