What is this discolouration?

[terrier]

This is my second grow with white widow seeds. These plants are stunted and yellow. The last grow was great but yield was small, so I added more lights. They were exposed to a lot of heat at first because of the added lights in small closet. I have made a new closet and 2 are getting better after fertilizing.
They were planted in "promix" soil mixed with worm casings.

 

[RobbieBurn]

I reckon a calcium deficiency, magnesium deficiency and high salt content (EC) in the medium. Feed CalMag after a flush.

 

[handjive4mota]

it's called Jive on the Hive, supposed to only affect bees.

 

[terrier]

Thanks RobbieBurn. Do you flush by just watering with no nutrients?

 

[The Germinator]

Doesn't look like a deficiency to me. Looks like what happens when you have high humidity and low air circulation due to transpiration.

 

[terrier]

"The Germinator" the plants were in a small closet, so that could be the problem for sure. Just built new tent for them last week. Two of them are getting better, I think, the other 2 are sick. Since starting them they all been bushier then what I remember the last crop being. The 2 that are healthy started looking better after giving them all some 2.72-1-2 fertilizer (low dose) after the move to new tent.

 

[The Germinator]

"The Germinator" the plants were in a small closet, so that could be the problem for sure. Just built new tent for them last week. Two of them are getting better, I think, the other 2 are sick. Since starting them they all been bushier then what I remember the last crop being. The 2 that are healthy started looking better after giving them all some 2.72-1-2 fertilizer (low dose) after the move to new tent.

Check on them in the dark period to see if you see water on the leaves. Or just before lights on. Mine did this when I had my fan on the light timer. The fan was shutting off during lights out. I remember the blackish look that your leaf pic has. My leaves would have water on them. But only if I checked with lights out. Good luck.