i would say the inline difuser is more eficient as what it does in terms of difusing co2, but a rhinox 5000 for example, placed in the right place( i.e under a power head/filter inlet) is probable just as good.
imo i would go for standrad 'stand alone diffuser'-way more cheaper than the in lines i have seen---http://www.greenleafaquariums.com/co2-diffusers/cal-aqua-diffuser-13mm.html#
If there is CO2 in the water then the plants can surely use that whether that is visable to them or not. Do you mean that the CO2 in a "mist form" would attach itself to the plants and enable better photosynthesis?
Going to have to lie own now and think about that one.
Having CO2 mist come in direct contact with the plants is definetly the best way to go. This is because you are bringing pure CO2 gas in direct contact to the leaves, so concentration wise it is many times higher in magnitude compared to the concentration of dissolved CO2 in water. It does require very good flow rates to get the bubbles around the whole tank, so normally works best in smaller tanks. Downside as mentioned earlier is that the tank does become full of bubbles.
thx guys for the quotes & threads - one thing that has not been mentioned is the positioning of the inline diffuser - water inlet pipe to filter or water outlet pipe from the filter. Mark has his on the outlet side but according to the diagram it clearly states to place the diffuser on the inlet pipe to the filter. Ed's thread does not state where the diffuser should be fitted either ie in which water line - external or internal lines.
Just to say - I've just converted from a ceramic diffuser to an in-line reactor and have had to turn my CO2 down quite a, even then I almost gassed a few fish and I struggled to get the level down enough so that the drop checker wasn't yellow all the time. Both reactors I made are outputting a very fine mist of bubbles too.
They are also placed in line with the output of the filter, that way cleaner water is going through the reactor chamber and it prevents the possibilty of an gas lock in the filter.
I've never found any benefits to using a reactor where the CO2 dissolves completely as opposed to micro-bubbles but look forward to reading Tom's work on it. The plants pearl really well and grow nicely so I'm happy!
Personally I prefer reactors as they need less CO2 to get to 30ppm, eliminate (or drastically reduce) micro-bubbles in the tank, get more gear out of the tank and need almost no maintenance!
Although I agree with James, one must be careful to avoid automatically associating the concept of misting with the technology of an internal diffuser. The misting technology is more closely associated with something like the Mazzei technology, which uses dedicated pumps and special high efficiency injectors, not necessarily with something as basic as a Rhinox or ordinary ceramic disk diffuser. As James points out, in much smaller tanks, the simple diffuser disk approximates the effectiveness of a Mazzei but as the volume increases the effectiveness of these simple diffusers rapidly decreases.