Because the hydropon and rock wool mixture will retain some water, watering once an hour for 2-3 minutes would be a sufficient feeding cycle. When the plants are very young the time can be reduced to every 2 hours instead of for every 1 hour. Watering in the night cycle can be reduced to every 4 hours. Many of the cycle stat timers now come with photocells and a night mode which will automatically reduce the feeding cycle for the dark periods. They are a definite must in any indoor garden running on an automated feeding system.