My suggestion would be to just add a little patience.
Give the plants some time to recover and see if the problem gets worse. In particular, notice how the new growth looks. The leaves that are already damaged won't ever turn green and look healthy again, even though the plant is in recovery. So to see if the PH adjustment fixed the issue check the new growth and see if that looks healthy.
I saw someone suggested that it's a cal mag deficiency. Not saying that it's not, but I think it would be unwise to make too many changes at one time because it will be more difficult to determine which changes did what for the plant. If it was only a PH problem then you don't wanna create a new problem by overdosing with unnecessary fertilizer. I use BioBizz myself, also with the light mix and I never add any cal/mag to my plants at any stage of the grow! I do have some rather hard water here though, so that might be why I don't need it.