[GrampsGrunge]

The optimum setup would be near the substrate, opposite the input for a canister filter so the water coming across the tank hits the front glass and diffuses downward in a semi chaotic fashion.


HOB filters tend to have inflows that angle downwards, and depending on the strength and depth of the water at the lip of the return "chute" of the HOB filter, there might be enough flow across the top of the water to force the slowly diffusing CO2 bubbles to move downward and outwards, once these bubbles get to the "mist" size it doesn't take much current to divert them from their trip upwards to the water surface.


Maybe place the diffuser off the side of the HOB inflow on the back glass so the CO2 bubbles can be naturally caught be the inflow and spread around more?

 

[GrampsGrunge]

Thank you both. I've got my diffuser as close to the substrate as possible. I might try positioning the diffuser closer to the intake as suggested... but wouldn't most of the bubbles get sucked into the filter as a result?

It certainly might but if the actual numbers of bubbles get sucked in is small, there's not much chance it will effect the overall diffusion rate, if anything it will help.


One of the forum members was using a bank of 2 liter DIY CO2 bottles and was diffusing the CO2 from this into the little siphon/air bleed hole in an AquaClear filter's impeller chamber.


I'd think any filter impeller would be fine as the strongly turbulent pass through the filter would further diffuse the CO2, and it's not going to kill your filter media's Nitrogen cycle.