First grow - Cotyledon undeveloped/yellow

[N.B.B.]

Hi All, this is my first grow and I seek thy counsel.
I have a 3 week old youngin' and her growth has stunted, one of the cotyledon leaves appears to be dying.

Setup Info:
indoor/soil
medium - coco coir (pre-soaked in water and micronutrient solution)
strain - Diesel Ryder from Joint Dr
water - local mineral (PH unkown)
watering frequency - every 2 days
light - cfl / sunlight (24hrs)
temperature - 20-25c
nutrients - applied for the first time this morning (NPK 8-3-4). 50% strength
humidity - unknown

symptoms:
The seedling was doing fine until wed/thurs when one of the cotyledon leaves started turning yellowish brown. The other cotyledon seems healthy.
The first two serrated leaves are visible but they haven't grown in the last few days.

Possible causes:
the coco may have been too wet for a couple days. I dried it out last night to counter this, but I can't really say anything has changed.

Nitrogen deficiency (the yellowing). I gave it fertilizer this morning (8-9 hours ago), but no response (yet).


I have attached 3 pics.

Could I kindly ask one of you to share your thoughts.

Any help is highy appreciated.

Thanks everyone!

 

[Fuzzy Duck]

If thats 3 weeks old it should be several inchs tall by now & have a few sets of leafs.

• PH of nutrient solution should be corrected to around PH 5.8 for coco for better nutrient up take.
  
• 1/4 strength solution should used intill a few sets of leafs have developed & would be more incline to feed from day 1.
  
• CFL with a light spectrum of Blue 6400k is suitable for veg/seedling stage.
  
• Plants need sleep 18/6, 20/4 is a lot better than 24/0.

I would find out your local PH of tap water whether that be hard or soft, this information should be aviable from local water companys website. I would invest in a PH meter to check final PH value of nutrient mix and PH up or down to adjust solution when required.

Cheap PH kits can be purchased for a few $$$ normally a liquid kit & PH colour chart.

 

[N.B.B.]

Thanks Fuzzy, I've got litmus paper en route.
I can't be bothered with a digital tester as it seems from a lot reviews it has to be calibrated all the time.

I'm also still waiting for my HPS to arrive. It's gonna have a light spectrum of 2000K which is not ideal for vegging, but it still ought to work. (or at least it works for others)

Thanks for the water company website tip.
I checked and it's around 7.4 which is way too high.
Let's see if I can get it down a bit.

Is it normal to have only one of the cotyledon leaves die?

 

[Fuzzy Duck]

Excellent news looks like you will be all on track soon.


Some PH down may be required to fine tune the end value of PH in your nutrient solution & litmus paper should be quite fine for doing the job.


Ye its normal for the first stage leafs to die from time to time if the seedling is not happy, purely a PH issue tho & once nutrient solution is adjusted correctly it will pick up in growth etc very soon.



Whilst HPS lights are mainly orange/red spectrum which is extremely popular for flowering it lacks a lot of the blue spectrum, unfortunaly this may cause plants to stretch & they may become long 'n' leggy.

Tip - You may wish to add a couple of CFLs 6400k to boost this spectrum of light to benifit the plants.


Alternatives you can use MH/metal halide for veg, i here of CMH/ceramic metal halides by philips to be dual spectrum some other brands which do dual spectrum are sunmaster & sylvania/grolux.

 

[N.B.B.]

Thanks again Fuzzy.

I'm starting out small. Experimenting.
If all goes well then I may go dual spectrum or just buy an mh, but these diesels are supposed to be short so hopefully stretching won't be a prob.