Rockwool vs Soil? Some advice if you would....

So I've been growing my indica dominant hybrid since this past June and I'm thinking that maybe using a rockwool cube in potting pellets is not retaining enough moisture? What do you guys prefer? I'm growing in SoCal towards the valley a little where it gets dry and hot and because this is an apartment my bedroom closet (grow room) does not get much cool or moist air, just dry hot air.

Would using potting pellets on top of soil be a better choice to help retain moisture when the plant is being fed? How often are you guys feeding and for how long? I've set my timers to 15 minute feeds @ 8am, 1pm, and 7pm....with lights on and off at 8am and 8pm (12 hour bud) Perhaps this is too much? I use a hydro system with a water reservoir located underneath the plant, the water is being pumped through a dripper that is fed into the base of the plant and I rotate the plant everyday to make sure every side is getting equal water/light.

Oh and also, the bottom leaves seem to be drooping and dried, what are the causes of this problem? I suffered some guttation earlier on already but is there any way to bring those earlier 3-5 finger leaves back to life?
 
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