Made of high quality materials, durable and reliable. With a non-return function to prevent backflow when the pressure change, which can protect the aquatic plant table and CO2 cylinder from damage. < /li> It can count the volume of carbon dioxide and provide enough carbon dioxide for plants. Easy to install and use, a good choice to make your aquarium different. Double head and single head are available, you can choose according to your needs. Installation method: Single head bubble counter: Remove the sealing ring and install it at the intersection of the trachea, and then tighten the bubble counter. Add 4/5 water into the bubble counter, and then tighten the top cover. Plug the CO2 tube and then tighten the trachea fixing nut. Double Head Bubble Counter: Add 4/ 5 Add water into the bubble counter, then tighten the top cover. Plug the CO2 tube and then tighten the trachea fixing nut. Features: Condition: 100% Brand New Item Type: Bubble Counter Material: Aluminum Alloy 0026 &; Acrylic Color: Silver Optional Type: Double Head, Single Head Double Head Size: Approx. 8.2 x 2cm or 3.2 x 0.8in (L x T) Single Head Size: Approx. 8 * 2cm or 3.1 * 0.8in (L * T) Package Weight: Approx. 32~34g Package Includes: 1 x Bubble Counter