hey mate.
what brand is coco, did it contain starter nutes? what exactly are u feeding? how much/how often? what ph range u running?
so u want to allow ur coco to dry out between waterings and dont over saturate wen watering. u only need a very small amount of run off. and water every few days as opposed to every day. if its cheap coco with high salt content, get a bottle drip clean from house and garden. that will rinse salts out and give a vitality boost. ph to 5.5 in veg. coco ph runs the same as complete hydro just about.
youre supposed to rinse the salt out of the coco when you buy it.
5.5-6 ph
for those size plants..id say 1.0 e.c.?
you could flush the medium heavy with filtered water with an e.c. of 1.0 (which i think is like 700ppm) and then let it dry out.
a solution with a e.c. actually flushes better than "pure" water becuase it has salt it in, which attaches to the salt in the soil and pulls it out.
might even want to try a lower e.c. of like .7-.8.