ISTA Compact V 3 in 1 Co2 Diffuser Bubble Counter Check Valve Aquarium (L) Plant These are the most practical diffusers available. Into a single piece, you have a check valve, a bubble counter and the diffuser. Also very important is that the ceramic plate can be replaced. CHARACTERISTICS: 3 functions in one unit: CO2 bubble counter, check valve and diffuser. Produces bubbles as small as a mist of CO2, generating maximum possible diffusion on CO2 in the aquarium. Undisputable quality and reliability. Compact size. Easy to install. For 4/6mm co2 tube (Does not contain) CO2 bubble counter, check valve and diffuser