Leaf tips curling up and discolouring between veins

Got a problem with leaves near the top of the plant curling upwards and discolouring between veins at first I thought it was heat stress or light burn as it was only happening at the top of the plant so I moved the lights further away but it is still happening they are 5 weeks in to flower and the bottom 3/4 of the plant looks perfect just a few leaves here and there on selected plants at the top. I've noticed it has started on other plants as we'll just on the top leaves curling up dramatically,discolouration between veins, effected leaves are going dry and brittle. The attached pic shows the discolouration but not the curling I'll try and add a more representative pic later

Room temp 26 deg,c / 50% RH
PH 6.5
in plagron batmix soil
Feeding plagron terra bloom full recommended dose
Plagron green sensation recommended dose

Could green sensation cause this as i only started to notice this just after I bought it the plants seemed fine up until now the bottle says use it along side your usual feeding program for the last 4 to 6 weeks I'm a bit stumped as to what it is I was thinking of cutting down on green sensation to see if the problem sorts itself out any advice welcome.

It may be a case of too much nutes locking out certain micros. It kind of looks like a ca. def. but it is not common in soil. I would give her a good flush and see if it starts to clear up.