Spot of leaves, the leaves are cracking

It looks since the question you have solved ur problem...for me its too low of rh and not enough light thats what gives me those same problems...also small pots

Looks to me like a root oxygen issue are you growing Kratky ? or has any of the air lines blocked in your dwc system ? I wouldnt say it was nitrogen because that usaually starts on the lower leaves and head upwards they the yellowing would be alot worse too if nitrogen what cal mag are you feeding her ? Coulc be too much or too little of that ph is fine temperture is not fine if your dwc an air temp of 28c will make your water 28c too so that will cause similiar symptoms to thing along with slowing growth dramatically too i know i grow dwc and its summer im having the same issues lol