Early signs of yellowing veins, dying leaves

[gwarf]

Hi all,

This is my first hydro (DWC) grow and my plants are showing early problems that I can't quite figure out. I've grown some cannabis in the past but its been in soil and outdoors.

Very early into this grow (about 7 days in) I started noticing yellowing in the leaf veins and the leaves started dying at the edges (photos below).
I've looked at several nutrient deficiency / toxicity diagrams but I can't identify this exact issue.

When I first noticed the problem, something that stood out to me was that the EC measured fairly high for how much nutrient solution I was using - this leads me to suspect either my tap water is somehow toxic to the plants, or I simply overfed them. I measured the EC of the tap water alone (without nutes) and it had a baseline of about 500 PPM (on a 500 scale).

I started off the grow with regular tap water and the nutes are GH Flora series.
As per the feed chart on GH's website, I started them on 1ml/gal of each FloraMicro / FloraGro / FloraBloom.

By day 7 I had ramped up to 4ml/gal, 4ml/gal, and 3ml/gal respectively. And that's when I first noticed the veins yellowing.

At this point, according to the feed chart, the PPMs should be around 500-650, but instead I was measuring around 1000 PPM.
PH measured 6.6, so I diluted the reservoir until I got the PH down to 6.1 and PPMs to 830.

Other measurements at the time:
Air temperature: 77F
Humidity: 75%
CO2: around 500ppm

I added 2ml/gal of CalMag thinking the yellowing was caused by a CalMag deficiency, but now I realize that might have been a mistake.
After adding CalMag the EC measured 1200 PPM, which seems way too high.

The problem continued, so on day 12 I replaced the reservoir with distilled water instead of tap water, and used a lower nutrient dose: 3ml/gal, 3ml/gal and 2ml/gal respectively.
After using distilled water, the EC measurement was more aligned with the expected value from the feed chart: 450 PPM.
PH measured 5.8.

However, I'm currently on day 17 and the situation has not improved much: the plant growth is stunted and I'm still seeing some veins yellowing in the new growth and leaves dying.
I trimmed some of the dead ends along the way.

Can anyone help me identify the problem? Maybe I overfed them? At this point I can understand if these plants are a total loss, but I'd still like to identify the issue so I can avoid it in the next grow.

Thanks in advance! Any advice is greatly appreciated!

(I saw a pinned post that said photos should not be taken under LED grow lights - so these photos were taken under indirect sunlight)




Here's some more info on my grow setup if that helps diagnose the issue:

System:
DWC using a small reservoir: 3 gallon capacity bin filled with 2 gallons of water. 6 plants per container. I don't expect the plants to get very large with this setup.
I use a small aquarium bubbler for aeration.
Lighting is a Viparspectra P1000 100W. Started at 25% power, ramped up to 75% over the first week. I measured around 17,000 Lux where the plants are.

Seeds: Random bag seeds. I'd rather figure out the kinks using bag seeds before I spend money on good seeds.

Germination: I rinsed rock wool and cut into chunks about 1/2-inch wide by 1 inch high and placed a seed in each chunk. As soon as they germinated I put the rock wool into clay beads in net pots and put them in the DWC system.

 

[OldMedUser]

You kinda screwed them up big time with the high nute level but now that it's more normal tho I'd start around 300ppm they should begin to mend so don't give up as yet.

Have they got roots extending from the net pots? Nice and white at this stage? You could try using a turkey baster to suck up some nute water and piss it down the net pots to feed roots still in there.

All I ever used in my DWC grows was RO or distilled and never added CalMag with fresh nutes but after a couple top ups with bigger plants I might add it at about half dose. I always used the AN pH Perfect so never bothered with pH. Top up the tub with RO, check ppm then add small amounts of nutes in the same ratio to get it back up to target then go away for 3 days. When the plants are small I never changed nutes until either just before flipping to flower or after the stretch. Was too lazy to change nutes so grew two tubs to the finish with no change at all and they were just as good. Adjusted nute ratios and amounts for different stages but never drained and refilled at all. Nutes lasted forever and weekly changes are BS so you need to go buy more sooner. Especially with small plants that barely eat anything. Might as well just burn cash.

After keeping track of ppm ups and down thru a few grows I found that the daily ppm drop could increase up to 4X starting a few days after going 12/12 until near the end of the stretch so give them some bloom booster like Big Bud a week before flipping, half dose, then the rest of the dose at the flip to get fast bud set and more sites. Extra light, CO2 and higher temps thru the stretch and they'll grow like crazy. Tehn feeding drops to levels like in late veg and slowly decline as flowering progresses. Use more K, Mg, S while much less N and P after week 5 or 6. Pot need way less P than K in flower and too much P gives it that 'chem' taste tho too much of everything will do that too.

This is assuming you get that far but I'm pullin' for ya!

 

[gwarf]

Hi OldMedUser,

Thanks for the info - good to know I just overfed them, that's something I can avoid in the future.

The roots are young but they reach the water and are still white:


I don't have a turkey baster but I use a big medical syringe / plunger thing for measuring nutes, I'll use that to baste them with water to rinse the roots.

 

[OldMedUser]

Hi OldMedUser,

Thanks for the info - good to know I just overfed them, that's something I can avoid in the future.

The roots are young but they reach the water and are still white:
View attachment 5127468

I don't have a turkey baster but I use a big medical syringe / plunger thing for measuring nutes, I'll use that to baste them with water to rinse the roots.

You should add some water and get it to just an inch under the net pots unless you're just holding the lid up to take that pic then carry on!

I should help top-watering a bit to get some to the roots up in the pots.

You want them to look like this eventually.

From this . . .



To this.