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Help! brown leaves first grow in growdrobe

Hi guys, been reading a lot of info on this site over the last few months preparing for my first grow and it's been really helpful. I decided to build a growdrobe out of 3x2s, hardboard and celotex 50mm board measuring 1.2 x 0.6 x 1.8m tall and put it in the garage. I've gone with a DWC hydro with 45l tote,  2 x 150mm air stone discs, 150mm net pot under a HLG QB260 LED light growing one plant with plan to do scrog later on. The grow started off alright, as I bought some feminised seeds off Royal Queen and went with White widow as thought it wouldn't get too tall, but now I'm on week 3 of grow and noticed that there are brown spots appearing slowly everywhere, starting at the edges of the leaves and then making it's way throughout the leaf until its half dry and crispy. This started at the bottom and worked its way up to the top leaves now. I've changed the reservoir twice, roughly every 10 days with RO water and AN Sensi grow A & B, but been really stuck for ideas as my EC is at 1.1 and PH at 5.7 - 6.1 with most the leaves are going half crispy then dying, leaving me with lots of half leaves. I've even tried adding AN cal mag xtra to no effect, thinking it was a deficiency. The only thing I can think of is that there's not enough airflow entering the growdrobe, as I have a 220m3/ hr 100mm inline fan pulling through a 100mm rhino pro carbon filter in the top right at the back venting outdoors and passive intakes (3 x 40mm waste pipes) in the bottom left intaking from garage (maybe not big enough?) I'm planning to fit a 150mm inline outtake fan and then use the 100mm inline fan as an active intake, taking fresh from outside to hopefully help with faster air exchange. I've also got a 4.5l humidifier in there, setting RH to around 55% and a circulating tower fan. I can upload some pics when I can figure out how to do it. Any suggestions would be very helpful, as I'm burning through electric for nothing at the minute. Cheers

Edited by 2toke

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Im going to take a guess here with the humidifier adding moisture and then your fan is drying the moisture up and therefore the leafs. Only other thing i can think of is the ro water and maybe your running low on calcium, i know canna say to mix 50/50 ro tap. Im sure there will be others to help along.



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On my first grow I had plants exactly like this when I would water everyday, before they had the root system to cope so it was just sopping wet coco. The leaves looked heavy and full and they developed that greyish necrosis starting at the edges and then working its way in.  The leaves on your plant look plush and heavy like they are full of water. I have never researched grown DWC and I'm probably not qualified to give out advice but I think you need more oxygen in your res probs.


If your res looks like a broiling bubble bath then I'd switch off your humidifier surely to god you don't need that in DWC, the leaves are your humidifier they exhale nearly all what they drink back into the atmosphere. If it is too humid the stomata won't open. If the roots are constantly drinking in dwc all that water needs somewhere to go.  Do you know what the RH is in the room as a whole rather than what you have your humidifier at?


Hopefully someone who knows about DWC will tell you whats up. 


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