OK - first off, apologies, as my digital cam isn't working...but I can describe the problem pretty well.

Set up - one female flowering for about ten days in an NFT system under 250 HPS, with an EC Meter reading of 1.4 consistently in both veg and flower. Water and grow-tent temps exactly where I want them. I change the water every 3-4 days. Plant generally looking in excellent health until about three days ago, when I noted bright yellow spots in the middle of just some of the leaves...not nute burn, as there is no curling or burning...yellow looks like bright yellow paint spots!

i'm thinking it's actually a nutrient deficiency, as EC read 1.4 yesterday and today read 1.3 and the ph went quite a ways up in less than 24 hours...so am I right in thinking that the girl is hungry? Am thinking of bumping up EC to 1.6 or 1.7...advice much appreciated from people who have confronted and overcome this problem, as otherwise the girl is looking great! most leaves a lovely green, and white hairs sprouting everywhere etc.
best
jash

Did you check UNDER the leaves to see if you got any bugs where the yellow spots are?
Your girls are not starving, although you could up the PPM/EC somewhat. I wouldn't change the water/nutes that often, perhaps every couple of weeks would be better. When you change the water that often, and if its not mixed right, then you can create more problems than you are trying to solve. Water temps all of a sudden change, EC/PPM is different.... all things they are forced to adjust to. If it gets worse, examine the roots, if they're not looking happy, then perhaps there could be a problem with oxygenating. I wouldn't panic, just keep an eye on them.

SN

cool, and thanks for your quick reply! i just checked under the leaves and all looks mite-free. i've raised the EC from 1.3 to 1.6, so hopefully i'll wake up tomorrow not to find the girl burned! interesting point about the water...perhaps it's not a coincidence then that the spots showed less than 24 hours after the last change?

finally, and this may be a weird one, but the leaves with yellow spots are the ones facing the full brunt of a desk fan...the leaves on the other side of the plant are simply gorgeous! the tent i'm using has, besides the desk fan at the bottom of the unit, a basic intake-outtake fan setup...

do you think I should prune the spotted leaves, or just leave well alone?

all best and thanks for your advice and experience!
jash

If the leaves are more than 50% "dead" then take them off, otherwise let them go.

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Yea, I would. A plant will naturally want to 'repair' its damage or disease, whatever it has ailing....but you are interested in growth and buds so eliminate the bad leaves.... unless there are too many, don't want you to strip the plant.... another thing you might want to watch is WHERE the leaves are that are yellowing... I've had a case where the leaves would yellow, mostly starting from the bottom of the plant and then traveling up from there and finally the plant dies. I don't recall what the problem was, but I finally fixed it by adding some hydrogen peroxide into the water..aeration... and it cured the ones that hadn't been affected too much

SN

thanks socialistpete and space needle! much appreciated! the spotted leaves are on the right hand side of the plant facing the desk fan, about three sets of leaves down from the top...so, just about the middle of the girl...will keep my eye on it...there are only about 6 or 7 leaves that are spotted, and only two of those look like crap so i'll get rid of those two and keep the other 4 and see what happens over the next couple of days...
best
jash

it could be a potassium def. possibly a magnesium or maganese def.

we are pretty much shooting in the dark here. if you fill out the troubleshooting form (in my sig) you might have a better chance at getting correct answers.

damage to leaves do not usually get repaired.


-shake

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troubleshooting form

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Do you think water drops could have landed on the leaves? If so they will act like little magnifying glasses under the HPS and bleach the spot underneath them.

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Shake hit the nail this time, fill out the form and if at all possible borrow a camera for a pic or 2. other than that we can all reply with " well it could be ......" and you be running around in circles and could possibly do more damage than good

OK, got a camera and will answer the following ... will include pix of leaves with bright yellow spots and healthy leaves...any additional advice much appreciated!

H=hydro
R=RockWool
D=NFT
E- tap water
E-between 5.8 and 6.1
HRT-1.7 EC
E-6 weeks
E-Canna Nutes Flora
E-250 HPS lights
E-day temps btw. 78 and 92 (temps fluctuate because of attic heat), night temps btw. 68-78
HD-Reservoir temperature btw. 70-75
E-Lighting schedule - 12 hours on, 12 hours off (2nd week in flower)
E-Type of ventilation - intake and outtake fan plus desk fan at base of plant

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it looks like you got some water or nutes on there and the lights burned them.

your temps are getting pretty high. are they in a box or tent and if so what size? are your intake and exhaust fan the same CFM?

and your res temp seems to be getting a little high. i'm not a 'dro guy though, so don't listen to me there. i'm sure one wil chime in.

did you soak your rockwool in pH'd water?


-shake

__________________
"happy trees"

troubleshooting form

"some of my sweets be tight and some of my sweets be fucked up, but all of my sweets gon' blow so killa smoke gets sucked up..." -Bun B

"But, when a long train of abuses and usurpations, pursuing invariably the same object, evinces a design to reduce them under absolute despotism, it is their right, it is their duty, to throw off such government, and to provide new guards for their future security." -Deceleration of Independence

Thanks headshake. i hope it's just water spots, as it's possible i dripped a bit from my fingers after they were in the res tank...and yes, the rockwool was soaked in ph'd water...i know what you mean about the temps, but sadly there's not much i can do about it other than spend money i don't have on an air conditioner which will further increase my carbon footprint! will maybe just do grows in cooler weather next time...
thanks again for your thoughts,
best
jash

Do you not see this problem in cooler wheather ?
If not it's heat. Your nutes EC kind of high. Even the good leaf looks a little crispy on the edges. I sprayed a foliar feed on some and that's kind of what it looked like plus the water burned yellow spots.