feeding schedule

i was wondering what a good feeding schedule is for my plants, ill have either 5 or 6 plants in a 4x4 tray, 40g res and i set the drain for about 2.75 inches. and is it bad that i set it for the 15m fill every 30m just keep the roots wet? if not what are some ways i can prevent the roots from getting dried by the light? thanks in advance.

What kind of planters/medium are you using?

My plants are in 3" cubes, inside net pots filled with hydroton, I feed 3 times/day with the pump running for 15 minutes.