2 Pack: Mineral Spa Frog Replacement<div style="text-align: left;"><strong>[Product Information]</strong><br><ul><li>Mineral cartridge contains silver and limestone.</li><li>Silver is the sanitizer and limestone neutralizes the pH.</li><li>Do not use non-chlorine shock.</li><li>Cartridge life will depend on spa size and number of users.</li><li>Minerals inside must stay wet. If they dry， unit needs to be replaced.</li></ul></div><img src="http://ecx.images-amazon.com/images/I/21eRry6RU1L.jpg" noproxy>