FWIW: someone at a pool and spa place that sells the pool filter sand told me that the sand was nice and sterile and clean but that she thought that the quality of the sand was such that it was not nice round particles but rather jagged and sharp edged so as to capture more of the detritus flowing out of the hot tub - the main purpose for this sand. Has anyone any experience with this?
The pool store employee was correct. New pool sand is rough, but not such that it would matter to plants, I don't think? The sand is microscopically sharp, but to my hand it feels like any other sand. It's certainly less course than sand used for masonry. It's recommended that you replace pool sand after a few years of "backwashing" a pool sand filter due to the sand grains becoming rounded and less efficient at trapping particles.