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.