Random burning, slight yellowing, leaf tips curling/dead

So I'm growing in a three way mix of
1/3 perlite
1/3 pro-mix bx
1/3 RO 707
15 gallon root pots

Anyway transplant was rough but that was 10 days ago and they seem to have recovered, the reason Im concerned is that im using this foil covered foam, and I have the foil facing in acting as the reflective material, the burning isnt uniform at all, one leaf even had a burn in a perfect line. Im using a 1000 watt mh but its about 4 feet from the plants tops.

I know that light is a little far from the plants but I figured the reflective material would compensate until they get taller. Now im thinking that the foil is creating hotspots. Its not over/underwater, and I just think that if its a nute deficiency it would be more uniform, some leaves are burnt, some are curling and look even a little N starved, most are normal (maybe just the very tips burnt) growth has been steady and predictable

Also worth noting that I made the horrible decision of not phing before I watered them in, though i used distilled water

I havent added any nutes since the pots are so large for the size of the initial rootball.

Question 1. whats with the random burn

2. since I have a nutrient light medium, but a lot of room for the roots to grow, when should I start hitting em w grow big?

Thanks alot in advance!

i dont wanna say annything because i dont have the knowledge to so, just gonna post this link i just found. so you can read and see pictures, until someone else maybee help you httpwww.growweedeasy.commarijuana-symptoms

its not always about how close the light is if the grow space itself is getting to hot. it looks like nutrient burn, or heat burn.

Thanks for the replies, since there haven't been any nutes added Im gonna feed w half strength Grow Big, i would be shocked if it were nutrient burn, since only 1/3 of the mix has any nutrient-rich additives and theyve been growing in there for a couple weeks. the temps in the mid 70s, good air flow, low humidity (been tryin to raise it beyond 35%) ill post whatever happens after 1st feeding