There is a good proceedural thread on RC from one of the German aquarists that helped with the origination of the working concept and how to get it to work without turning the tank into a septic soup of pelagic bacteria. Keep in mind that free organic carbon is food to anaerobic bacteria, and some of the anaerobes are facultative in nature, meaning that they have the biochemistry on board to use this substrate either without or with O2. With O2, they can get from about 16 to 36 times more energy than without O2, allowing them to freely reproduce at about that many times their normal growth rate with that extra energy. Dosing with alcohol needs to be done very carefully, and with a slow acclimitazation to the presence of this carbon fuel source.
Ken, not quite the same mechanism as using GAC: GAC works by adsorbing free organic compds and some ions (DOC, Gelbstoff, terpenes and terpenoid compds and the like) that literally by their presence increase the turbidity of the water column. These organic substances are adsorbed to the surfaces of GAC to effectively remove them from the water column until all the surfaces and the pores of the GAC are filled. Th function of GAC is a physical direct effect of the carbon mass on the organic molecules.
The addition of ethanol to the system increases the metabolism of anaerobic (actually most) bacteria so that they will work harder to convert nitrate, etc. into nitrogen gas and misc other intermediates in the nitrogen cycle: feeding them 2-carbon fragments increases the need for more nitrate, much the same way that when we run (as opposed to walking), we use more oxygen to burn the carbon (6-carbon sugars, etc.)we use for energy that our body needs to fuel muscle contraction. This same mechanism or alcohol fueling the bacteria is used in wastewater treatment for sewage, etc., but these septic systems can use methanol (much cheaper single carbon fragments) that would poison our live systems of vertebrates and invertebrates. The net result is a drop in avaiable nitrate, making our systems nitrate-limited rather than phosphate-limited for algal growth, clearing the water of pelagic algal growth and most often reducing overall algal growth in the system. Sounds great until you overdose the tank with EtOH and you get a
bacterial bloom and resulting O2 drops... ...and it doesn't take much, we're talking mililiters per dose...
The effect of ethanol on the tank is indirect, via nutrient reduction and subsequent decreases in algae and misc. other nitrate-dependent growth organism populations that live pelagic lives suspended in the water column. This water-clearing mechanisms is slower to occur, but in the long run is just as effective, however it carries many caviats and potential disaster issues that carbon does not.
Sorry Ken, I couldn't let it go by...
