Purple punch autoflower

Using 12 stage r/o water, water temps are in low to mid 70s. problem seems to be on lower leaves. I use cal/mag

Was there a point in time your ph was off? On old lower leaves I usually ignore unless I see the problem spreading. Old damaged leaves don't repair so always look to new growth to see if a problem has been corrected. 🤘😤

looks like calcium/magnesium deficiency. Are you using RO water. if so you should be adding calmag or something similar.