How often should I turn on my drop system??

[Old Resin]

If you water every 4 hrs for 15 min-and your ph is good-and some of your plants are doing OK-and some are not-and everything seems to be in order-more nutes. The ones that are fine will take it-and the ones that are doing poorly, probably need them. At the size in the pictures, you should prolly be between 300-450 ppm-possibly as high as 600 ppm depending on your nutes(I'm not familiar with the ones you are using). Also, some would say that your buckets are too big for those small plants. Rule of thumb is 1 gallon per month of life.