i used the bioring mod on my otto powerhead, with the co2 line attached to its venturi (similar to rio's). it seems like the co2 is mistier. it's been running for only 1 full light cycle, so can't tell if it's helpful to the plants.

however the flow appears to have slowed somewhat and the noise of the otto has gotten louder. i'll have to trim the bioring down a little more to reduce the noise. if that doesn't quiet it down i'll try to drill small holes in the impeller.