What's causing this?

600w HPS
Foxfarm Big Bloom and Tiger Bloom following the feeding schedule on their website.
Foxfarm Ocean Forest Mix
12hr of light

A few days ago I noticed one of the five girls had definite nutrient burn so I flushed that one and gave all five of them a couple days off the nutrients. I have since resumed giving them all nutrients and the one with the burn at half dosage. Is the above picture a nutrient deficiency possibly? This is not the one that was burned.

This one looked fine until I backed off the nutes, then it started to do this. The one that actually had the nute burn to begin with, that caused me to back them off, looks the same and hasn't worsened at all.

Is it definitely nute burn then? Should I back off the nutes again because they worsened when I did that before.

It is natural in the phase your in that you experience a nitrogen deficiency and you want that to occur because the needs of your baby requires more phosphorus and more potassium. Fox farm products are wonderful but I always use half the recommended dosage and I have an alternate water and feeding schedule in place. The question is when you flushed how much of water or flushing agent did you use in comparison to your container medium size.

I used 3x the container size of water to flush. I have also started alternating the water and feed schedule. So I don't really need to worry about it anymore?

Nitrogen. N is the most common deficiency of cannabis indoors or out. The first sign is a gradual, uniform yellowing of the large, lower leaves. Once the leaf yellows, necrotic tips and areas form as the leaves dry to a gold or rust color. Symptoms that accompany N deficiency include red stems and petioles, smaller leaves, slow growth, and a smaller, sparse profile.

looks like the necrotic tips and slightly yellowed lower leaves is N deficiency
may also be caused by sever ph lockout but it would have to be severe since nitrogen is hardest to lockout with high or low PH

Thank you Phinxter. I'm going to try a ph test tonight when I get home since they looked worse this morning.

Ok the soil ph appears to be a little above 7.0. Now, instead of the leaves curling down like in the picture they are curling up including some of the smaller leaves. I still have about 4 weeks to go...am I going to be alright? They seem to be getting a little worse every day. Maybe it's heat stress? Typically I'm between 82 and 85 deg at the canopy, but it can peak up to 87 or 88 deg if the room stays closed up for too long.

can anyone help?