These are the best air stones out there. They are weighted so they naturally sink. They can be taken apart so that if they were to ever clog, they can be cleaned or replace the disks outright. They also work great inside sponge filters. Really they are the best air stone money can buy. Instead of replacing a cheap ceramic air stone every 4-6 months as they get worse and worse for bubbles, install one of these once and nearly never worry about it again. Tighten or loosen the disks to change how big the bubbles are.