This small device sets up a mini cyclone internally that dissolves and diffuses CO2 throughout your tank. It is very small, about the size of a woman's palm, but can put enough dissolved CO2 into a 125 gallon tank to support massive plant growth. It has a 65 gph motor and can be positioned at the bottom of the tank - easy to hide! It's simple to clean and has excellent flow control. And it's fairly inexpensive, I paid less than $35 for mine which made it one of the cheapest components in my CO2 system.