Leaf burn help

Been gradually raising my feedings from 300ppm in veg to about 800ppms in flower now
It’s been 7 days since I flipped to 12/12 and I noticed some new growth looks kinda burnt or something
Does anyone know what this is
My hlg light is 30 inches away and at 60% power so I doubt it’s light burn
3 gallon pots with coco and fed once a day with runoff
I have flushed and fed with 500ppm hope to make sure it doesn’t get worse
I also tested my runoff and it was at 400-500 ppm so not bad but the ph was closer to 6.8-7
I feed at 5.8-6 so I fed today at 5.6 to see if it helps
Any recommendations I’m new to coco
Also using remo nutrients supercharged kit at half dose

I’m no expert but if I were you I’d try just giving it plain Ph’ed water, watered till runoff.Seems to me like some sort of lock out.

I did that yesterday and watered today with lighter nutes
I was under the impression never use just water in coco
Always feed after a flush

I think my pots went to dry for a few days and from what I read when coco drys out it messes things up.
Could that be it?
I water everyday when lights come on by hand with 20% runoff
But can hardly keep up with how much they drink