I have not used it in hydroponics yet, the idea just came to me a couple of weeks ago. I inquired with the manufacturer and they said indeed it is a good product for hydro, it looks like road gravel. They have an internal void of 50 %. Stalite said it was able to create a LARGER root ball than the expanded clay balls were capable of. They also said there was one downside and that was it did not wick up water as well as the clay. I assume the clay balls are more porous and the slate is a true rock and only draws water with larger capillary action and does not become saturated, for lack of a better word. During the expanding process or heating of the slate, lime is used for some reason, I was told the rock needs to be soaked and then rinsed before using it. I linked a pamphlet about it sent to me by Stalite in the post with my pics. On the east coast its sold at most Concrete Ready Mix suppliers as a light weight aggregate, and its dog crap cheap. You just go down there & tell em what you want, they scratch their heads and depending on how you talk, they may say no problem (do concrete talk southern style) then take what you want or they may charge a modest fee, I always leave 20 bucks.. If you buy it at a store its called vole block, permatill, it works for lots of different things, but what I meant to say is they will ask about 20 dollars for a bag of it. But I have found bags for 5 dollars less the pretty pictures. So it can be free, or five dollars, or 20 dollars, or buy it by the ton 100 to 200 dollars. I have used it a lot in planting trees, and other landscaping projects for a very long time. Just wash it first, maybe use some weak acid, as in whatever you think weak acid is. It's verified non toxic and organic whatever that means, it can not make water hard if washed and its ok for aquarium filters. Great to put some in a plastic pot with a composted potting soil.
