Purple stems looks like Nitrogen. Burnt tips looks like potassium... looks like nute-lock. I don't see any perlite in the soil? Looks very dense. Your soil might be holding water too well and since you haven't watered (which flushes nutes though), the nutes make salt deposits which block the roots from absorbing what they need. Shitty problem (speaking from experience), cuz you need to water but your plants have too much, already. A repotting maybe risky with them in that condition, but might be the best option. Unless someone has some way of managing it that I don't know about. I have a method that worked for me but, My plants weren't that bad. I can't say how full-proof it is. If the drain holes in the pot are flush with the bottom of the pot, you can sit it on a few paper towels to try to suck some water through. The paper towels will just keep absorbing as long as there in contact with the soil. When they're totally soaked, put new ones and do it some more. Good luck.