Wanna hear something funny? I have heard mutterings of growers using- NOT KIDDING- fibreglass insulation as a medium. I'd treat it exactly as rockwool, soaking it in quite a large excess of water set to pH 6.0.

I've never used the shit but would be interested to see someone run an experiment with bagseed to see if you can get seedlings to survive the requisite ~10-14 days or so from germ to the time when they are rooty enough to go into the hydroton. Actually, a little plug of fiberglass in a net pot of hydroton, hand-watered until they root enough to go into your automated system.

Chances are there's some fibreglass poking out of the cracks atop your basement sills... lol... you on;y need a tiny piece. Who's up for an experiment?