Hmmm...so you are basically just aerating the water the rockwool is sitting in? The Rockwool does need a correct pH..I don't see why this would kill the roots...I mean if the rockwool was sitting in standing water that wasn't moving it would be an issue...this is like DWC, but shallow...so Shallow Water Culture...I don't know what will happen though, so if you have more seeds than this one then try it, but if you don't then I would just plant the seed, or just leave it in the cube on a plate or whatever til you are ready to put it in whatever you want to put it in...