Leaves with dark & light green splotches

Not sure what's going on here. At first I thought it was just that the tallest parts of these plants are too close to the light. But now I'm wondering if something else is going on. I've looked through all of the plant nute deficiency pictures and don't see anything like this.

The discoloration began at the top of the tallest plants where they were bending up toward the light but is now very very very slowly moving down. The rest of the leaves are a normal color

Setup is DWC with 400w HPS.
Using Flora Nova Bloom at about 750ppm. pH stays between 5.5 and 5.8 on its own.

The girls are very crowded in their space. They pretty much quadrupled in height/width when I switched them to flowering. The crowding and proximity to the light can't be changed right now (maybe next round). Best I can do that I haven't yet done is get a fan pointed directly at the tops. Right now the fan is just providing fresh air and a slight breeze in there but not much gets to the tops.



And here is a wide shot so you can see the shape of the rest of the leaves. Harder to see the color in this shot but I assure you the leaves are a 'normal' green and not at all splotchy.

Should I provide more info or something?

I noticed today that there are a few small leaves much lower on the plants that have this same discoloration. There will be just one leaf like that and the rest around it are normal.

If it keep spreading (yellow) without curling of the leaves it is a nute issue. This would indicate a sulpher deficiency and even an iron deficiency. For the sulpher part, mix 1 tablespoon of epson salt (horticulture) to one gallon of ph balanced water. water with this every other time. As for iron goes, folier feed with chemical fert containing iron or rusty water. Allow a good week for changes to occur. During this time period be even gentler with ur regular feeding. If giving half, move to 1/4. Just for the time being... Good Luck