dont know much about hydro but i know one good thing about it is you dont
have to guess on nutes,you put in what works n your good.

as for temp 90f is a lil high ,are you sure thats the highest temp you get in a day?when you said "appears to be drying" makes me think the temp is getting to high.its good to get a high/low thermometer ,it will record the highest the temp gets in a day,
you just have to reset it after you check it.90f wont kill them but much more than that n you start getting problems.i think i would try to find a way to bring the temp down to around 80 at least.

good luck peace