Included with all Under Current systems, the Aqua-Pore Anchors replace the large O-ring in the bulkhead nut. The Aqua-Pore Diffuser slips under the feet of the Aqua-Pore Anchor on both sides of the growth module and is anchored from movement or floating. The Aqua-Pore Anchor is available in 2? and 3? for all 8/13-gallon systems. **Suction cups will still be included in all Aqua-Pore Diffuser kits, but are not required with the anchor kits.