RDWC BROWN SPOTS PROBLEM

Hello.
Those girls are same clone in RDWC system.

Grow area : 1.5m x 1.5m
Temperature : 23-26 celcius
Humidity : 55-60%
Co2 : 1100 ppm
Light : Resina Q bar 700 watt
Light distance : 45 cm
Nutrients : Advanced nutrients connoisseur full line
Current EC : 3000 μs/cm ( i am not going to go higher than 3000)
Ph: 5.5 - 6.0
water temp : 20 celcius

I keep getting the same problem at this week of flowering. Beginning of 4th week from 12/12.
I change reservoir every week . I add Sensi Cal mag to RO WATER until my EC goes to 350-400μs/cm and then i add nutes.
I keep getting the same problem despite i tried different nutrient companies in the past ( GH, Remo nutrients).
The problem starts at the leaf tip creating small spots and spreading until leaf is like burned and crispy.
I am assuming it is light stress . any help ?

I don't know much about your nute line, but that EC seems real high. I normally have the EC about 1400-1600 max. Wondering if you are getting a lockout?

i have strong light with high co2 plus they are clones and heavy feeders. The 3000 ec is the highest i go with this clone , i know it sounds high but it is just in the beginning of the week . During the week i add just RO water so my ec is coming down everyday. It could possible be nute burn .

Looks like nute burn to me.. I never go above 2 EC..

Thats a calcium deficiency and major stress. The calcium issue is a hard one i am battling myself when running high light levels and Co2 ,yours is most likely from running too much cal mag and general base nutes and its causing potassium and magnesium to compete with calcium. High light levels and CO2 put a very high demand on the plant so your nutrients has to be super dialed. Hard to give specific advice but i would lower the EC to 2 and raise the light a little to get a bit less demand on the plant.

shouldn't have any deficiencies at 3EC

and i'm pretty sure your room temps are way too low with that high a co2 ppm level.

so i could maybe low the ec , light power and co2 concentration ?

i wouldn't change everything at once.

co2 at 1500 ppm should be room temp above 90F

my plants would die in a day at 3EC . i usually run around 1EC . you'll have to figure out your optimal EC with your conditions

Just to avoid confusion with EC scales , He is running 3000 μs/cm which is not 3EC but 1,5EC.

rkymtnman said:

shouldn't have any deficiencies at 3EC

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High feeding rates does not mean you cant get deficiencies, excess cations in nutrient solution will compete for uptake by the plant and lock out other in the process.

Nifty420 said:

Just to avoid confusion with EC scales , He is running 3000 μs/cm which is not 3EC but 1,5EC.

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3000 μS/cm = 3 dS/m = 3 EC

devorg said:

3000 μs/cm = 3 dS/cm = 3 EC

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Ah yes i see i made a mistake trying to calculate it from ppm's ! i think you did aswell?.
3000 μs/cm = 3mS/cm(3EC) not 3 dS/cm
3 dS/cm =300mS/cm

hey guys thx for the answers.
I've changed the reservoir on sunday. sunday EC was 3000 μs/cm.
Today ( Tuesday) . EC = 2600 μs/cm.
Spots seem to not spreading those 2 days.
I ll change the reservoir next sunday , and i will lower the EC to 2500μs/cm

Nifty420 said:

lock out other in the process.

Click to expand...

that was what i was getting at.

Nifty420 said:

calculate it from ppm's

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he/she didn't give ppms though. and it's not always a 0.5 conversion rate

Biancoverde said:

hey guys thx for the answers.
I've changed the reservoir on sunday. sunday EC was 3000 μs/cm.
Today ( Tuesday) . EC = 2600 μs/cm.
Spots seem to not spreading those 2 days.
I ll change the reservoir next sunday , and i will lower the EC to 2500μs/cm

Click to expand...

i know that you are using RO but have you ever tried just the base nutes and see if you need to add extra cal/mg?

rkymtnman said:

i know that you are using RO but have you ever tried just the base nutes and see if you need to add extra cal/mg?

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you have a point cause my base nutes contains cal-mag . there is a big chance that is a lockout from excess Ca.
i will do this on sunday when i change reservoir.

Biancoverde said:

you have a point cause my base nutes contains cal-mag . there is a possibility that is a lockout from excess Ca.
i will do this on sunday when i change reservoir.

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on the base nute labels, what is the listed % of Ca and Mg?

i used to use RO and i only need to add extra Mg via epsom salts.

rkymtnman said:

on the base nute labels, what is the listed % of Ca and Mg?

i used to use RO and i only need to add extra Mg via epsom salts.

Click to expand...

calcium 2,2%
magnesium 0,7%

Nifty420 said:

Just to avoid confusion with EC scales , He is running 3000 μs/cm which is not 3EC but 1,5EC.

High feeding rates does not mean you cant get deficiencies, excess cations in nutrient solution will compete for uptake by the plant and lock out other in the process.

Click to expand...

That's completely wrong. It seems you're confusing EC and the derived ppm scale (usually 0.5, sometimes 0.7, or 0.64)

1000 microsiemen = 1 millisiemen

3000 microsiemen = 3 millisiemen