Quote Originally Posted by LOC NAR on probation
(The plants sit in small four inch pots with aquarium grade stones.)

This is the only thing I would question. You sound like your doing your homework well. And trying many times with same results. Those stones sit too close toghether and do not hold water for a cation exchange. The roots by flower time may be like root bound and choking off by then. That's why they do good in veg, plenty of room.

I would go with another medium. Hydrotron or rockwool or lava rocks just to see. You have studied and tried almost everything else.

Do a search here for Loc Nar. I started with drip system with 6 plants to a 5 gallon tub. Only when I change nutes did I have to down my PH for a day or so.

Pic's of plants and roots would help greatly. You have come too far to give up now. If you over come this it's bud city. And what's the lights and heat in your room and rez ?
Roots look to have enough room. The tubes are 80% full of water and they sit in the solution and no light seems to be getting in. Roots look healthy as well. Sorry for double post but I can not edit the above post for some reason.