Betta Airline Regulators are for controlling the supply of air to various devices into your aquarium. These include air stones, air-driven filters, ornaments, CO2 diffusers and some Protein Skimmers. These are all compatible with our 6mm silicone and plastic Betta Airline to help you create a set-up of your choice. Supplied as 2 items on a card, 12 cards per outer, to be sold separately.