Hi mate, I think this is magnesium and calcium deficiency. I could be wrong. It is usually what comes up first in a ph caused lockout. Make sure you PH is between 6-6.5 and the temp of the water is between 66-72'F. You should start to see improvement soon. You could add some agricultural gypsum to stabilise the substrate. I hope this helps, plenty of experienced growers here willing to help. Good luck and happy growing.