4 Week Old Casey Jones Deficiency?

These were clones taken roughly 4 weeks ago. Used rapid rooter cubes, transplanted into a mix of roots organic and roughly 30% roots 707. Watered with RO ph of 7 PPM 40 for first 2 weeks. Started using Calmag roughly 2 weeks ago at a rate of 5ml/gal. They are under T5's.
This popped up about a 2 weeks ago and has seemed to get worse on the bottom's but not so much on the new growth. I've got some super lemon haze in the same setup clones taken at the same time etc. that are doing just fine, really good I might even say. I do however also have a few Afghani's that started showing what looks to be the same symptoms as the Casey Jones.
I'm haven't run soil in years, I feel totally out of my element again. I've been running various hydro setups with relative success for a while now.
Any help would be greatly appreciated as I'd like to try to save this batch if at all possible.

That looks like ph prob or a nute salt build up on the roots or all out root rot.

looks like fert burn to me

Thanks for the replies guys I appreciate it!
I kinda doubted it was nute burn as I've used virtually nothing but calmag at the rate of 5ml/gl. I added 1 ml/gl floragro 1 watering last week thinking it was deficient, didn't really seem to help or hurt.
I do think it may be a ph prob as haloman said. I read in the newest Rosenthal handbook that Roots Organics soil has a low ph of something like 4.5 if I remember correctly.
I made a slurry with a cup of ph 7 RO water and roots soil, and it tested at just under a ph of 5. Now I know this is far from scientific but it seemed to somewhat confirm Rosenthal's testing.
That being the case should I simply up the ph of the water? Or is there something else I may be overlooking?
Thanks again

Back to the top...This forum moves quick!
I may have contributed to the problem with slightly overwatering, particularly last week. I've since backed off.
Any other advice or possibilities? Thanks again in advance.

Your ph seems very low. I keep mine in between 6.5 and 7.5. I have no problems except damn bugs.

The ph of the roots organic straight out of the bag is supposedly around 4.5 or so. I'm transplanting into larger pots today, using approximately 30-40% super soil in the bottom. Just tested the super soil in a slurry mix with straight RO water with a ph of 7. It tested to roughly 6.5-7. I plan on using roots organic soil for the top layer. Any way to correct the ph? Or any advice as to what I should do?
Seems a lot of people use roots soil, anyone else seem to have similar problems?

It don't look burned or over water something else maybe? It could be anything cuz over watering or root rot they weren't have the brown like it does. Too too many variables in dirt and since coming here a few time in the last week or 2 I'll say 90% of problems are in dirt 10% in Hydro? I'm going back to rock wool you can use it just like dirt but ph ur shit to 5.8 Water it when it light weight and give a little flush each time feeding every other watering!