I won’t go deep into the scientific area of this. I’ll leave this to others who are more comfortable with this topic. To make a long story short, the goal of dosing Vodka is to provide an organic carbon source to grow bacteria in order to consume phosphates and nitrates. Bacteria are then exported via the protein skimmer and so is the nutrient that it consumed. The idea here is to reduce Nitrate and Phosphate to create a better environment for the fish and invertebrates and reduce the chances of an algae outbreak.
Even though there is scientific literature to back up the idea, this dosing method was achieved through experimentation and observation. Many fellow aquarists shared their results and observation on forums to finally come up with recommended dosing rates. In general, users note a dramatic decrease in nitrate and phosphate molecules, while others note increased coral coloration and clearer water.
Note: This method should do well for systems that do not effectively remove NO3 and PO4. Systems with very low levels of NO3 and PO4 may not benefit to any great extent by dosing carbon.
Phosphate and nitrate are the two main nutrients reduced when adding organic carbon. Basically, dosing and other kinds of any organic carbon would give you the same results.
People have also experimented this with vinegar, sugar, etc (all of which are organic). The reason we use vodka in comparison to other spirits is that vodka is purer in composition. Vodka is mostly water-ethanol: no additives, no flavor added, etc.
How does it reduce NO3 and PO4?
By adding organic carbon, we increase bacterial growth and reproduction. The reason why we do this is that bacteria use nutrients such as nitrate and phosphate to build new cells which result in rapid NO2 and PO4 reduction. Like us, they need their carbs. Bacteria are then exported via the protein skimmer and so are the nutrients that it consumed. Most vodka users note a notable increase in skimmate production, removing more waste than without vodka addition.
A good skimmer is a key requirement for this method (here is my favorite one). Cultivating bacteria to lower NO3 and PO4 is one thing but you also need to remove those bacteria from your system. If you keep the bacteria in your system, they will eventually set those nutrients free when they die. You can’t rely on water changes for that so make sure you have a good skimmer! The other reason for using a skimmer is gas exchange. The increased bacterial biomass will decrease your dissolved O2 levels which can cause stress (or death) to the reef inhabitant.
1. Your first step is to test your system’s NO3 and PO4 levels. Do not try this method if you don’t know this!!!!!
2. Estimate the net water volume of your system. The water volume is the sum of the aquarium volume, the sump, and refuge minus live rock displacement. It is ok to underestimate the net water volume but it is risky to overestimate it.
3. Start with 0.1 ml of vodka per 25 gallons (100 L) daily for the first three days.
4. Then, double the daily dosage to 0.2 ml per 25 gallons (100 L) for days 4 to 7.
5. On week two, add an additional 0.5ml to the daily dosage, regardless of the aquarium volume. Always test your system’s NO3 and PO4 levels. If your NO3 and PO4 levels start to drop during that 2nd week, maintain the current daily dose. If your NO3 and PO4 do not drop, add an additional 0.5 ml of vodka to the daily dosage on week three. Add 0.5 ml to the daily dosage every week until your NO3 and PO4 start to drop.
6. When your NO3 and PO4 levels drop near undetectable levels, cut your current dose in half. This will be your daily dose.
7. Keep dosing vodka every day (the dose on point 6) and keep monitoring your NO3 and PO4. If levels become detectable again, increase your daily dose by 0.1ml per week until the levels start to decrease again. Your NO3 and PO4 levels will eventually drop back to undetectable. This will become your new daily dose.
NB: Those instructions are for 80 proof vodka only (40% ethanol by volume).