Beach sand can be almost 100% quartzite, almost 100% coral, or anything in between. Quartzite is fine, but coral raises the KH continually. Pool filter sand has to be relatively clean, almost uniform, and not adversely affect the pH/KH of the water, so it is ideal if you want plain sand. Play sand contains lots of very fine particles, which are not desirable. Blasting grit, like black diamond, has uniform particles, is relatively clean, and is not quartz or coral, so it is generally good. But many people have used many different sands and had good success with them.