Brown stains on leaves, look like birthmarks

Hi growmie dont panic it don't seem so severe, just check your pH and EC maybe you are a little bit off in those, I would use low EC around 300ppm on that stage and try to get pH at 6

Your temperature to humidity range is important in all stages of growth. here's a little chart that's explains things better then I can. I like to use. http://www.just4growers.com/media/23631/vpd_2degree.gif

1000w can run hot and create a low humidity range in the room so check that values and correct them if the humidity is too low r if the lamp is not to close. I would also have cheked the bottom of the basket to see if the roots are hitting the water as the clay balls seems a bit dry to me. Last thing is the ph as you've already checked but in that kind of situations you need to check every days even couples times a day

If your ph is 6.2 should be fine. I’m a soil grower so that’s in a Comfortable range for me. I believe hydroponic set ups operate on a slightly lower ph. 6.2 maybe a bit high for soiless. Not sure though

Had the same thing happening early in my growth and I concluded it was a calcium deficiency. I used some cal mag with regular PhD water and they did fine. Didn’t show up on any new growth. I specifically used “MagNifiCal” from remo nutrients

I just got a PH test strip and it says 6.2. so PH should be ok? Any ideas?