Hydroton/Buildex grow rocks

[TOMMY]

Hydroton/Buildex

Heres a follow-up. The salesman for this company called me from NC and told me that they ship it on rail to the local concrete company <lightweight block division> here in Augusta. So I was able to go there and drive off with a dually pickup load for 30 bucks. Never having seen grow rocks and going by online pics, they look rust/orange in color? The product I have is blue/gray in all shades from light to dark. There are some pieces that are orange/rust but that seems like a glazing that's on some of the rocks. It has as many holes it as sponge. Its a kiln fired shale...some pieces are rounded like grow rocks in pictures but most are in gravel shapes <not pea-like but like septic tank fill aggregate>.The sizes range from 1 inch to fine pieces in the shake. They weigh half what gravel does at least. I have not tested the pH, but it being a fired rock, I am sure its neutral. My question at this point is, what size should I screen it to <how large are grow rocks> and are grow rocks nice and round? None of these have sharp edges, but I could put em through a tumbler if it were necessary. Also if you dont mind, I will send a few of these rocks to you and have you check them out. They probably have these at a concrete company near everybody... Tommy