Seedling yellowing on new growth

First up this is my first indoor grow. Seedlings pictured here are Skunk #1, CBD Shark Shock and Tickle Kush. They were all germinated at the same time 7 days ago and put under a 6500K 150W CFL 3 days ago on a 18/6 timer with a oscillating fan. I am using a seedling mix of coco and no nutes as yet.

To my (as yet) untrained eye this looks to be burn from the CFL? I originally put them within 2" of the globe as I have read is the best position.

Any ideas as to the cause and or advice to get the them back on track? Or is this normal growth?

Examples of the yellowing.


Light setup now as I have raised it to around 4-5" above were I can't notice any heat now when I put my hand at the same height as the seedlings.

What are your temps?

They have varied wildly due to freak weather. Low and high over the past 24 hours have been 55f and 85f respectively. Also I don’t have an extraction fan as yet if that helps. Was only planning to get one once in veg as I am only using cfl at the moment.

To be honest seedlings can be weird little things sometimes yet grow to be a strong healthy plant.

The yellowing is either due to rapid growth, sulphur or light being too close or simply nothing at all, just doing it's thing.

Are you sure that light is 5" away? looks more like 8-10 to me.. I keep them about 3-4" away when they first sprout. Get a measuring tape if you're not sure but for a 125 thats a bit far away, hence you see them stretching their little legs to reach that light

Nutty sKunK said:

To be honest seedlings can be weird little things sometimes yet grow to be a strong healthy plant.

The yellowing is either due to rapid growth, sulphur or light being too close or simply nothing at all, just doing it's thing.

Are you sure that light is 5" away? looks more like 8-10 to me.. I keep them about 3-4" away when they first sprout. Get a measuring tape if you're not sure but for a 125 thats a bit far away, hence you see them stretching their little legs to reach that light

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My height was a bit off, readjusted with a measuring tape.

They were stretched like that before I put them under the light.

A 30 degree temp change indoors? Wow. Except for that, you may also want to consider LED instead of CFL. You don't need an LED grow light, you can easily find LEDs that fit normal light sockets. If you can only find 100 Watt equivalents, go to a hardware store and get a double socket adapter for a buck or so and use two 100W bulbs (you can get the bulbs there too). CFLs aren't too bad with heat and I used them for quite a few years. But LEDs give off almost no heat and can get quite close to the plants. I keep mine about an inch or two away. Different if it's an LED grow light though.

Way to big of a temp swing man. Your shocking them big time. Get your temps consistent or expect things to get worse.

A quick update as I seem to be on the right track by sticking to the basics.

What I have done to try and correct the issue:
1. A tossed my old el' cheapo PH meter and got a proper hydro grade meter. After calibration I noticed I was watering at a ph of 7. Far to high for a soil less medium.
2. I started introduction nutes at seedling recommendation, again I was not aware I need to start nutes so soon with soil less.
3. Started to better manage the temperature fluctuations at night/morning.

Results seem to be in the right direction, time will tell:

Skunk #1 (left) 3 days ago .vs (right) today, color is stating to show at the veins. After much research I think this may be boron lockout due to the high PH. Also makes sense as boron is not moveable and the reason its at new growth.

Looking good man! They’ll only get stronger and healthier from here on out

Hi all sorry to jump on this. Having a similar issue. You all think it's the same as above?

Temps were at 27.9 in this pic as I left heat mat on!

Generally lows of 20 highs of 26
No nutrients given just gerninated into Rockwood then into biobizz light mix

FEED !!.

jimihendrix1 said:

FEED !!.

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Thanks for the reply man.

Really? Is it not too early? Was advised biobizz light mix has enough go keep seedlings going for 3 weeks. These are only 3 days into he mix?

What would you feed?

Anyone else have an opinion on this?

Have put a picture below that o have just taken of all 6

Had exactly the same issue. Totally agree with Jimi:

jimihendrix1 said:

FEED !!.

Click to expand...

My PH was way out of whack, maybe worth recalibrating your meter? I am running 2ml of BioBizz grow per 1ltr for feed, since then they are starting to recover! Also using a PH of 6.0 and allowing it to drift to 6.2 now with great results.

Either way its related to lack of nutrients, more than temperature IMHO. The ones I caught earlier recovered quicker.

jeffvader said:

Had exactly the same issue. Totally agree with Jimi:



My PH was way out of whack, maybe worth recalibrating your meter? I am running 2ml of BioBizz grow per 1ltr for feed, since then they are starting to recover! Also using a PH of 6.0 and allowing it to drift to 6.2 now with great results.

Either way its related to lack of nutrients, more than temperature IMHO. The ones I caught earlier recovered quicker.

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Cheers man.

Total noob! Going to invest in a decent ph meter then!

Anyone got any recommendations through use? Prefer that to sponsored Google reviews haha

Appreciate you replying though thanks man

DankGriff said:

Cheers man.

Total noob! Going to invest in a decent ph meter then!

Anyone got any recommendations through use? Prefer that to sponsored Google reviews haha

Appreciate you replying though thanks man

Click to expand...

I opted for a upper mid level meter. After talking to the guys at the local hydro store I settled on a HM digital Ph-80.

My reasons for purchase were quick reading and ease of calibration over the other at the same price point. As an outdooor guy trying my hand at indoor a meter next to lighting was perhaps my most important buy.

Final update for others who may have the same issue as I had.

The ladies are doing well after PH and nutes. 2nd and 3rd pic are a day apart, showing some decent growth and return to color.


Nutrient uptake has slowed, I suspect this is due to high humidity (70-80%) I have been having.


Thanks to all who assisted me in this thread.

Whats your temp? it should be around 68F