Yellowing Leaves

This is my first ever grow I am growing 1 Blue Mystic Auto under 270 watt LED light.I am at 4 weeks flowering and have noticed a few leaves are yellowing.Just wondering if anyone would have any ideas what might be causing this.Any information will be greatly received.Thank you.

looks like it needs nitrogen.

if i were to guess that is the more developed side of a nitrogen defeciency. plug those babies into the nitro socket and watch those leaves produce a nice, lush green color once more.

It doesn't look like nitrogen deficiency to me. Nitrogen deficiency starts at the bottom of the plant since nitrogen is mobile and travels from the bottom leaves to the top leaving the bottom ones yellow. This looks like maybe magnesium..

How long does it take for the leaves to get back to normal once you put them on the nitrogen/mag?

never. the ones that are damaged aint comin back jack but all the other leave and new growth will be green as grass. also if it is an isolated mag def then you can use 1 tablespoon of epsom salt per gallon of water. or you could foliar feed with a solution like 1 tablespoon per liter. I dissolve mine in a cup of hot water first then add to the feeding solution.