Vinegar and or vodka are fine choices for dosing organic carbon. Ethanol (vokda) oxidizes to acetic acid( vinegar ) which moves on to acetate.
There are some differences:
Vinegar is more dilute 95% water and 5% acetic acid . This standard white vinegar has a pH low enough to prevent bacteria from consuming it before it's dosed. 80 proof vodka is 60% water and 40% ethanol; the alchol content keeps the bactria from growing. In terms of carbon content 80 proof vofka is 8xs stronger than vinegar because there is less water in it. The extra volume for vinegar may be important to some for auto dosing setups for smaller tanks.
Both vinegar an vodka drop pH from bacterial activity and CO2 production. However, vinegar does this precipitously when it's dosed. Vodka does it slowly. When dosing vinegar the dose should be spread out over a long period of time during photosynthesis to offset the CO2 the acetic acid releases . Vodka can be doed all at once without a precipitous pH drop.
The extra volume may be helpful when dosing via an automated system. On the other hand bolus dosing is convenient for my routine. FWIW,
I've been dosing both about 70% vodka and 30% vinegar for over 5 years with good results.
Phosphate drops first in my experience contrary to that of others noted. It's quite logical for it to do so.
The heterotrophic facultative bacteria that consume the organic carbon assimilate dissolved nitrogen and phosphate as they grow . These 3 nutrients are then removed as the bacteria are skimmed out. Since these bacteria are facultative, they grow aerobically. Then when oxygen is used up they function anaerobically going after nitrate for the oxygen leaving just N ;some of which binds with other N molecules to form N2 nitrogen gas which bubbles out of the tank reducing nitrate even further than the reduction due to nitrogen uptake from assimilation.
The ratio of 116 C: 16 N: 1 P allude to earlier is known a the Redfield ratio. It is an enmasse measure for phytoplankton in the sea. Specific organisms vary to some degree in terms of these proportions;some significantly.. Even if they didn't organic carbon dosing would ultimately reduce nitrate more than the proportion to phosphate in the ratio because the anaerobic reduction occurs in addition to the assimilation providing an extra exit for nitrate ; there is no such additional reduction for phosphate. Over time some find it necessary to use gfo or other removers to deal with low range phosphate ; some dose nitrate to enhance PO4 consumption and avoid nitrogen deficiencies.
Zero PO4 andor zero NO3 are not good goals ,imo. and ime .I get good grwoth and color and little to no nuisance algae with Po4 in the 0.02 to 0.03 range and NO3 at around 0.2 to 1pmm. Natural surface seawater runs abut .005ppm Po4 and 0.2ppm NO3.
To those considering organic carbon dosing , this thread may help you decide on the method and or whether or not you want to do it at all:
http://www.reefcentral.com/forums/showthread.php?t=2134105&highlight=organic+carbon+dosing
