[Robert Hudson]

It is not the turbulance per say, it is the length of time the gas remains in contact with the water. In a chamber with a jet stream, the bubles remain trapped until they are dissolved. In a bell, the bubbles may sit there a while, but can be pushed out from the bell when you try and raise the amount of gas...know what I mean? The bell can only handle a very low flow rate. A reactor can handle a very high flow rate. Other types of diffusors like the Eheim are glorified air stones and a total waste of money. They become clogged and dirty easily and quickly and no matter how tiny the bubbles may be, most simply rise to the waer surface and are disapateded.

I think the bells date back to Europe when it was thought all you needed was a very small amount of C02 in your aquarium, like 10ppm max.