5pcs Aquarium Air Pump Check Valves - Non-return One Way Valve For Fish Tank. Aquarium Air Check Valve Enhance the Safety and Functionality of Your Aquarium Setup with Our Aquarium Air Check Valve. Specially Designed for Standard 3/16 Inch Airline Hoses, This Essential Accessory Ensures the Optimal Performance of Your Aquarium's Air Pump by Preventing Water Backflow. While Perfect for Oxygen Aerators, It is Not Suitable for CO2 Systems. Key Features: - Application: Compatible with Standard Aquarium Air Pumps and Airline Hoses; Not for CO2 Systems. - Function: Protects Air Pump by Preventing Back Siphoning During Power Outages. - Connection: Features a Directional Arrow for Easy Setup; Connect Input to the Air Pump Hose and Output to the Air Stone Tube. - Troubleshooting: Easily Clear Any Blockage by Gently Inserting a Toothpick or Paperclip from Input to Output. Ensure Your Aquarium Remains a Safe and Healthy Environment for Your Aquatic Pets with This Reliable Air Check Valve..