CO2 bubble counters allow you to monitor the flow rate of CO2 into your aquarium. Being able to visually monitor the CO2 flow rate helps detect possible drifts due to faulty regulators or needle valves. The bubble counters are attached inline with the CO2 line and secured to the outside of the aquarium. Typical bubble counters allow the user to monitor CO2 flow rates up to 4-5 bubbles per second. Flow rates higher than this makes counting, and therefore monitoring, difficult to impossible. Cal Aqua Labs' Double Counter addresses this issue by offering a unique dual-function design that allows monitoring of both low and high CO2 flow rates within one unit.