Leaves get crispy because they will fall off, the plants are focusing their growth on buds and not on maintaining its fan leaves.
letting the medium dry is what you need to do when using coco, the plants only need to be watered when the first few inches of coco is dry, its to stop you from overwatering your plants and it will also make sure the plants sucks as much of the nutrients as it can before you go and water again.
If the nutrients too strong your babies will tell you, I personally havnt gone above 1500PPMs with my grow even though the chart I have says to sit around 2000.
If they grow fine at smaller doses then no need to load them up.