plant problems with pics help needed

Wondering if someone could help me out a little here. They are 3 weeks into flowering and having some issues. I am using RO water and nutes are only at 600ppm and looks like they are burning but not sure if thats what this is or not do to the nutes not being high at all. The first three are of one type of plant and the last pic is of another witch seems to be having another issue as it is good and green but has leaves curling under.

...what's that pH like?
...have you used any cal./mag.?

Ph ranges between 5.7 and 6.2 and no on the cal./mag. I mix my own nutes from talking to fatman on here and I would ask him as it is his mixture but he hasn't been on here for a while. From what he has told me it is a complete mix and doesn't need cal/mag. Is that what the problem looks like?

...that's my first thought. Have a view at attached pics of cal. def.View attachment 1064190
View attachment 1064189