Junior Poster
Jan 23, 2005
I have a 2nd CO2 cannister and was setting it up and had a question. Is it preferable to feed a CO2 line into a submerged powerhead or place one of those special diffuser stones so the bubbles flow into the current generated by the powerhead?

In Walstad's book, she touts the importance of emergent growth to allow for increased CO2 uptake. Seems to me the whole mist idea, by allowing CO2 bubbles to contact the plants, is bringing emergent growth to submerged plants.

Tom Barr

Staff member
Jan 23, 2005
Re: Venturi

Few scapes deal with emergent growth, but allow it access to the air is not an option for many plants, we keep submersed plants generally. Having some floaters in my tanks was something I did nearly 30 years ao, that is hardly new.

Wetlands and our tanks are quite different as are the goals.
Emergents are good for the access to the CO2 in the air, but do little for most of our tank layouts.

The mist notion is different from this.
Mist is both gas and liquid CO2 underwater.
Gas diffuses much faster than liquids.

In a certain sense, the emergents are similar to the idea of increasing diffusion rates with gas vs liquid, but the mist is both.

Mist is also nearly 100% CO2, emergents can grow even faster, if you add pure CO2 to get about 1800ppm or so in the air which is only about 380ppm CO2.

Tom Barr