Is this magnesium or potassium deficiency??

[psychoman671]

Hi everyone,
This is from a HSO blue dream going on week 4 of flower and has started developing these brown spots on the leaves. Growing under a 300w marshydro LED. any input is much appreciated! Thanks guys!

 

[Dan Ultra]

It looks like you are in the very late stages of Magnesium deficiency. Are you supplementing Cal/ Mag since you are running LED? Are you in hydro using RO or watering soil with RO water? Are we looking at older fan leaves or new fan leaves? What is the pH of your medium?

The more info you give us, the better we can help you.

But going from this pic, and assuming its older and larger fan leaves, I would say Mag. Mag is a mobile nutrient so you will see deficiencies develop in older growth first. With the lighting of the leaf in between the veins and now with the addition of spotting, it fits Mag pretty directly.

Magnesium also stimulates the uptake of Phosphorus, so you might be locking that out a little as well.

 

[psychoman671]

Thanks for the response ultradan!

I've been suspecting a mag deficiency but wasn't too sure if it really was. This blue dream plant has been growing under LED for a total of 8 weeks total, 4wks veg and 4wks flower, but I have only been supplementing with calmag since the 1st wk of flower.
I'm watering using tap water and growing in fox farm ocean forest. I also recently got a ph pen and ph'd my tap water and it was at 7.8, could this contribute to the problem? Also , I just ph'd my runoff and it was at 6.4(but this was after flushing with 6.5ph'd tap water, forgot to get an initial runoff sample)
As for the mag deficiency , should I just keep with the calmag feeding, at 5ml/gal, or should I supplement with something else? Epsom salts?

 

[4fingerlidday]

I run led and use Cal-N-Mag with every watering at 4 or 5 ml per gallon with RO water, not sure on the Epson salt, but a mild dose could help to bring up the levels, hope some one chimes in on this

 

[Dan Ultra]

I would keep with the CalMag feedings. Epsom salts might mess with the pH of your medium

 

[2clean]

Hi everyone,
This is from a HSO blue dream going on week 4 of flower and has started developing these brown spots on the leaves. Growing under a 300w marshydro LED. any input is much appreciated! Thanks guys!

I noticed bad things usually happes around week 4 and 5.. I would flush then start with half the same feed with added cal mag. then go back to regular feeding.. looks like cal mag,check ph first.