Assuming he's using jack's at the proper ec and PH he shouldn't be having any nutritive issues. Definitely not a K deficiency. Add magnesium to that list. Jack's 5-12-26 has 6.3%. There's no way you're going to see a deficiency when jack's is applied at the recommended rate. Without more info it's not possible to diagnose further. I have no idea what his PH or medium is like. I'd still lean towards LED light burn. There should be no nutritive issue if he's using the 5-12-26 and calcium nitrate at the recommended rates. Tip burn is possible when running a high ec with jack's, but there should be zero reason for a deficiency. Lot's of people like to monkey with the jack's ratio though for some reason unbeknownst to me. It rarely ends up a happy story. Who knows? Maybe he's using his own formula. I've never seen anything but LED light burn and magnesium deficiency cause that kind of chlorosis and necrosis. Again with 6.3% mag sulfate in the jack's there's no way he's experiencing a magnesium deficiency. This is all assuming he is following the proper mixing instructions.
I will try to answer all uncertainties :
1. i'm doing DWC 70L totes with 50L water in each, i mix my res up in a separate 120 L tote before dividing between the 2.
2. My recipe for the 100L is Jack A- 95g B-63g salt 25g ( i will now moving forward omit the salt until flower has set in).This
3. Ph 5.8 currently although it was crept up slowly to 6.2 over the grow.
4. I do have a small grow journal should anyone want to check it out, it does at least document my progress so far.
res temp has been in the low 70's-high 60's.
5. tent temp had been a little cool last week 65-75, its now 75-83. ( i had been venting outside, switched to inside as i was pretty sure LED wanted higher temperatures.
6. humidity levels 50-55%, just lowered it to 45% as she's about to show signs of flowering any day and i thought that would be better.
again thanks for the input