Bubble Counter

A Bubble Counter is a small glass or acrylic inline device placed in the CO2 tubing between the regulator and the diffuser, filled with water that allows individual CO2 bubbles to be counted as they pass through the unit. By counting bubbles per second, aquarists can reliably calibrate and reproduce their CO2 injection rate — typically targeting 1–3 bubbles per second for most planted tanks — without relying on pressure gauges alone.

Glass bubble counters are particularly prized in the aquascaping community for their aesthetic quality and inertness — unlike acrylic units, glass does not discolour or develop scratches that obscure bubble visibility over time. Borosilicate glass versions are especially durable and resistant to the slightly acidic CO2-saturated water they contain.

The bubble counter also functions as a visual confirmation that CO2 is flowing from the regulator, providing immediate notification if the cylinder has emptied, the solenoid has failed, or a kink has developed in the tubing. It is typically positioned at the regulator end of the tubing for easiest visual access from outside the aquarium.