Professional DIY Kit: a complete system in 4L size bottle, that includes SUS304 stainless bottle, regulator, precision needle valve, and easy adjustable bubble counter. Safe: the bottle body is made of 1.5mm thick SUS304 stainless steel (25% thicker than normal 1.2mm bottle); it can sustain pressure up to 80kg/cm2 (or 1137 PSI); safety valve will open automatically when the inside pressure exceeds the safety threshold. Needle Valve with Bubble Counter: high precision, aquarium specific needle valve provides accurate fine-tuning; steady 1 bps is achievable; bubble counter with check valve built-in; it stops water from back flowing into your CO2 tank (protects your CO2 tanks from rust and corrosion). 12V DC Instead of AC Power: having the solenoid on a timer, you can specify when you want CO2 injection on and for how long.