Fluval Bio CO2 500 (Low-Pressure CO2 System, up to 250 L) is an easy and safe way to add CO2 to medium-sized planted aquariums. It uses a yeast-based fermentation process to generate a steady supply of CO2 gas, providing plants with an essential nutrient for growth without the need for pressurized cylinders. The Bio CO2 250L system is simple to set up and maintain, operates at a low safe pressure, and helps achieve lusher, healthier plant growth in freshwater tanks (approximately up to 65 gallons).