Need help with these

I have been feeding them at around 600+ ppm ph perfect sensi grow with b52 and voodoo juice also calmag cause there in coco ph is 6.0 of water still have problems seems to be progressing slowly but I wanna stop it before flower cause I know it will most likely ruin them. any ideas on the problem and solution I was thinking of dropping the b52 and just giving them a full dose of the sensi with voodoo and calmag.

anyone got anything

it looks like past damage. leaves will look different when they die off. some will have brown spots or decaying a bit. or some just turn yellow and fall off.

the top of your plant as well as the main growth looks clean.
Don't stress unless it moves up the plant.
the first leaves of a plant never survive till the end.