Coco grow in a 3x3 tent with a 300w mars hydro light. They were looking pretty good so I started mainlining them a few days ago. I also bumped up the dimmer to 75% per user manual. The leaves are crispy. RH stays around 60% and temps in the 70’s. I checked the pH and ppm before and after run off and it’s all in range. I was thinking the light burned them. The last grow light I worked with was a 150w so o thought maybe I turned it up to high. It hangs around 24 inches high. Now looking at them tonight the jack herer’s new growth is now doing this and I dimmed the light to 65% yesterday. They were looking good and overnight they changed drastically. I put 5ml of cal mag in a gallon of water with the other nutes and pH balance to 6.5. Any help would be greatly appreciated!
What is “in range”? The readings (numbers) are the most helpful so we can help steer you right.
Your leaves are kind of twisted, usually pH wonky - what are you growing in?
So 300w at 24” at 75% (math is eluding me right now- 225 w?) that sounds too intense at this stage. Any chance you have Photone (phone app)? It’s time to get light meter readings from your canopy.
Oh - there we go. Your pH is off.
Also what nutrients are you using at what levels? (PPMs and dosage)
Coco needs 5.8(ish) pH - it’s different than soil and requires the Hydro level of nutrients and pH. That’s gonna mean lower on both usually. Is it straight coco?
I haven’t tested the lights but I backed it down to 60% Sunday. It’s 70/30 coco perlite mix. I’m following the general hydroponics high frequency fertigation feeding schedule (everything but SM90 and rapid start). I have been following the ppm and pH on this chart until a yesterday because I read and found a chart showing that around 6.5 pH calcium is absorbed better. So I was trying to fix it in case of a calcium deficiency. I do agree that it looks like pH imbalance after more searching and looking at pictures. I was staying in the range at the bottom of the feeding schedule so maybe my pH meter is inaccurate. When I tested my run off it would also test in those parameters. I put the schedule I have been following along with the chart I recently came across. The plants did start to look this way before I increased the pH.
I think what @Graysin was referring to with the PH and Calmag was the order of nutrients mixed. The calmag is mixed in 1st, then nutrients, then PH?? 
5.6-5-9
I was just pointing out that 6.5 Is way too high for coco, but that’s a great catch on mixing order - it most definitely needs to be
Silica → mix → CalMag → mix → other nutrients → mix → microbes.
@Em honestly just remove the damaged leaves and raise your light higher up and see if the damage reappears. The feed schedule looks kind of timid to me but I don’t know enough about the nute line to say that with any certainty at all. It’s probably light burn and you’re chasing a problem you don’t have and creating new ones by altering your pH and adding nutes she may not need (although CalMag is hard to overdo so it shouldn’t matter if you add a bit extra).
Test the DLI (download Photone and check your light intensity) - it will confirm if the lights are too much.
I also thinks he’s got you going in the right direction. Young plants can have a hard time with lights too intense.
I do see a spot on 3rd picture lower right bottom plant that looks like tobaccoing which is normal.
The others like @Graysin said, can be cut off with no worries.
Keep an eye on the new growth. It may or may not start growing out a light green but will fill in a darker green as she grows.
While GH has good products and schedules, I would highly also recommend visiting coco for cannabis dot com. It’s all about coco.
Also, if unsure about something, ask first before doing something. There are a ton of folks here that are more than capable of helping.
Good luck and keep’em growin! 
Are you revegging these?
That’s the website I reference for everything.That’s where I got my feeding schedule.
No I recently started mainlining them.
I really appreciate everyone’s help! Now I don’t feel like I’m totally messing this one up. I’m going to stick with the feeding schedule unless I find an updated version for GH. I’ll test my grow light asap and I plan on investing in a better pH meter. Looking in there today the new growth on 3 of them are already showing signs of the same problem.
Are youbusing General Hydroponics nutriebts trio Grow -Micro - Bloom right ?
@Em if so check out @NUG61 garden ?
You can get the same results , google the lucas formula calculator for General Hydroponics nutriebt system and start there for what week your plants are in and do you have any calmag ? 5mls of calmag to a gallon with the Lucas Formula and good luck keep it green and Clean @Em you can do this !
What would the light Intensity need to be at?
DLI
Veg 20 to 30
flower 38 to 65
PPFD
100 to 300
400 to 600
800 to 1000
I hope these are correct, let me know. lol
Definetly looks like deficiency based on roots. Specifically that whiteish discoloration of the leaves. Like others have mentioned 5.8 is where you want to be. You can try flushing with ph water at 5.8 until the ph of the water coming out of the pot is between 5.8 and 6. This will reset the ph in the soil at the roots. Then like most mentioned once it dries out feed it starting at about 1/2. Test the PPM and PH of your overflow. The PPM should be a lot lower and ph should be good. If ppm is dropping nicely then increase food mix. The guide on the food is based on if you have perfect commercial grow conditions. Your exact ppm you will need to find based on your specific setup.
The run off has been about 5.7 pH and 350-450 for the ppm the last several days.
Yeah that’s what I’m using along with the 5ml of CalMag. I’m also using silica, diamond nectar, and H2O2.
Why are you using peroxide? It’s gonna kill anything beneficial you’re growing in the root zone
It’s the last on that feeding schedule and it’s supposed to be beneficial by oxygenating the roots. But I can stop using it. I didn’t use it my last grow
I personally would not proactively put hydrogen peroxide in anything except my bud wash. I use it to treat mold, mildew, and root rot if absolutely necessary, but even then I prefer using beneficial microbes like bacillus before I revert to H2O2.
Are you in hydro ?