Check your PH and make sure it is dead on before doing much else. You say you are using 4x4 RW so that makes things a lil easier about watering. RW hold onto water really well. Pickup a dry RW 4x4 and get a feel for how heavy it is, pretty light huh? Now pickup one of the RW blocks with plant and feel the difference. Also when you pickup block does water start pouring off of block or not. You say that you flood 2-3 times daily, that should be fine with my exp. I used to use the 4x4's but no longer do and when I used then I flooded up to 5 times a day for 15 mins a shot. I know you said temp and humidity is fine but what are the numbers?