I'd be surprised if you over water this since it tends to drain quickly and wont hold as much water as soil, or coco for example. if you can rig up a drip system that might be the way to go. Fill your containers and pick them up, now water them and pick them up again. You should be able to tell the difference in weight pretty easily. You'll want to water when they feel light. This sound ridiculous but it works for me. You'll probably have to water every day or every other most likely, possibly more once you have roots in there