Need help with this leaf. Yellowing between veins.

[KSum]

Hi, this leaf had a spot on it for about a week, then almost overnight it turned into this..

I've looked through various threads to help identify the problem but I didn't see anything that looks quite like this.

PH is around 5.8
Temp stays between 65-78
RH stays between 48-62

They are potted in 3 gallon pots with about 2 gallons of Fox Farms Ocean Forest. I've been giving them Jack's Classic 20-20-20 at 1/4 strength in veg and just started Jack's Classic 10-30-20 2 days ago. I know it's probably a nutrient problem, I just haven't seen which one it might be.

As always, any assistance is greatly appreciated.

 

[NuttyProfessor]

5.8 is a bit low ( i think ) your locking something out 6.5 is a better range

and how close is your light , it could be bleaching

 

[KSum]

I'll double check the ph in both the soil and the water (with and without nutes) and see where I'm at.

The light is about 16-18 inches above the tops. (600W HPS with wing reflector) This leaf is the only one on the plant showing this and it's one of the first fan leaves at the bottom.

 

[KSum]

In looking around some more there are several other leaves on that plant that are showing the same signs, as well as one of the others. So it's a common problem between them. The edges of the leaves affected are curling under, which you can kind of see in the picture above.

Soil : 6.5
Water : 6.8
Water w/nutes : 5.6

I'm thinking maybe to much nutes.

 

[KSum]

After using Google to search some more images for possible causes, it looks like it may indeed be light burn and/or heat stress. For a few days I was unable to keep the temp around the tops of the plants under 85 during the day and it would drop to 62 at night. All of this with very low humidity during the day. ( less than 40% )

I've got the temp stable during the day at 76 and the RH around 50% but the 2 plants showing this plus the edges of the leaves on many of the plants curling underneath suggests these to be likely causes. I'll raise the light some and see how it goes. If it starts to spread to much more then I'll know it's something else.

None of it looks like nute burn though. Deficiency maybe, but not burn since that shows up at the tips and edges of the leaves first.

 

[iGrowX]

Definitely a deficiency of some kind, excessive wind too maybe that over dries the leaf ?