As long as you are pumping plenty of O2 into the water in your res you probably wont have to much of a problem with overwatering but a lil voice in the back of my head says you might want to check into a 15 min interval timer. Also if there is any way to change how the lights are mounted to the board so that they sit horizontal then you will get more light to the plants. CFL's put most light off of the sides then they do the end of the bulb.