leaf has brown spots

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

Hi there, first of all i would like to ask whats your water temps? Dwc is a great system but increases the possibility of root rot. If your ph is at right range, and u dont overdo it with nutes may be u have root rot. Where I live is a hot country so deep water culture is a no no, most of the times I got root rot due to water temps. Smell the roots if something is wrong u ll understand it instantly. If all are good, which I honestly hope are, change your reservoir with a lighter nutrient mix. Also I would strongly recommend, as I use Advanced Nutrients also, see the whole product series for grow and bloom.

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.