CO2 is a crucial nutrient for plants. The plants will have a hard time thriving without a CO2 supply. Add extra CO2 to the plants in your aquarium with Tropica CO2 System Bio. For best use of the product, a temperature range of 68- 77 degrees F is recommended. CO2 System Bio - CO2 supplement, activator (5 portions), CO2 diffuser, gasket, air cap, hose, suction cups.