What did you use for a substrate for the plants to grow in? I've bought some clay balls (not sure what they are called, they are about 1/2" diameter.) But, since then, have tabled the idea till I have the time, space, and mental energy to put into doing it right, and learning the system. I'm a confirmed DIYer, so... tend to make things quite complicated cause I'd rather learn how to make it myself than buy a ready to go set up.