First set of true leaves yellowing

[Rudy]

Hi there.
Not the first time grower but experiencing this for the first time.
I have 2x Creme Bubbly from Mephisto and 2x Colorado Cookies from Dutchpassion sown 6 days ago.
They are in easy plugs and were looking fine until one cookie and one cream produced first set of true leaves.
They are looking yellow deformed and, compared to the other two, undeveloped. Cotyledons look perfectly fine.
Seeds were in the dark until sprouted then put under the 600W MH sunmaster lamp at the distance of roughly 70cm(28 inch) with 20/4 light regime.
Temps are moving from 20° in the dark to 27° with light turned on and humidity around 45-60.
It's a bit dry but I keep the plugs moist so I don't think it's the humidity issue.
My guess is a too strong lamp but I've done it before with same setup without problems.
Any advice would be appreciated.
Here is the picture (two top ones with the problem):

 

[Master_gRoshi]

thats a new one to me. Typicallyi see the button leafs yellow not the new growth.
Let me tag a few folks that would know much better than i would.
@Waira @pop22

Just make sure to tip well lol. Just kidding man.

Hope your babies get healthy soon

 

[Master_gRoshi]

are they in a dome? to keep humidity up?
are they on nutes yet?

 

[GoAuto6]

Try moving your light up? What pH are you watering at? The other to from the picture look like there gonna turn soon. Soilless medium is treated like hydro and should be ph'd to around 5.5 - 5.7

 

[TehSnow]

I'd say pH, I had a yellowed stunted seedling like that too.

 

[Arthur]

I'm guessing your right about the light height being the issue. Little to no stretch showing... 600w hps is quite a bit for seedlings/sprouts... we'll wait for the A teams responce, but if I had your light in my tent, I'd have probably started closer to 40-45 inches.... unless you have a dimmable ballast. Am running my first cob grow, just 200 watts, I'll be dimming that by half till the ladies look like they can take it.

 

[Rudy]

No nutes yet, I thinks it's still early.
I removed the dome when I put them under lamp but I might cover them again and move light up a bit and see what happens.
You think it's ph this early and with no nutes?
And other two looks fine which is confusing me even more sine they are all treated the same.

Sent from my Nexus 5X using Tapatalk

 

[Rudy]

Oh and easy plugs are made from organic materials and have predetermined pH value which is retained even after adding water or nutes with different pH value so I'm pretty convinced it's not pH.
I hope this can be solved

Sent from my Nexus 5X using Tapatalk

 

[Rev. Green Genes]

I'm guessing your right about the light height being the issue. Little to no stretch showing... 600w hps is quite a bit for seedlings/sprouts... we'll wait for the A teams responce, but if I had your light in my tent, I'd have probably started closer to 40-45 inches.... unless you have a dimmable ballast. Am running my first cob grow, just 200 watts, I'll be dimming that by half till the ladies look like they can take it.

even for full grown plants I'm 20 inches with HPS/MH any closer and we're eating crocodile teeth tacos for dinner.

Seedlings could stand to be 40 or more inches with a 600, they are not using much of the light anyway.

 

[Rev. Green Genes]

Oh and easy plugs are made from organic materials and have predetermined pH value which is retained even after adding water or nutes with different pH value so I'm pretty convinced it's not pH.

This is not really the case in real life. They can make it sound pH balanced, and maybe under lab conditions it is. But anything you add to any medium changes its pH. If your water is 7.5 and your using soil-less medium at 5.5 you will change the pH. The challenge is to get a clean measurement. Waira always recommends the 'accurate 8' pH meter for soil and soil-less use.