Pondmaster Air Stone Set · 4 pieces is a Pondmaster-branded product in the ownkoi catalog. Set of four weighted ceramic round airstones from Pondmaster. Sold as a replacement set for diaphragm-pump-driven aeration kits. Specifications and pricing reflect the manufacturer-published or retailer-published data at the most recent catalog refresh. Verify the live listing on the source retailer page before purchase.