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By James Gasta


One of the newer trends in lowering dissolved waste in marine aquaria is by carbon dosing.  Carbon dosing is an effective means of increasing heterotrophic bacteria by a controlled feeding of a carbon source. 

 How Does It Work?

 Increasing the beneficial heterotrophic bacteria (bacteria that feed on dissolved nutrients such as nitrates and phosphates) population in the aquarium water by dosing a carbon source will increase these bacterial colonies to a level that will effectively remove nitrates and phosphates from the water.  Large colonies of beneficial bacteria can only exist with a controlled feeding of an organic carbon compound at specific intervals. This process can take three to five weeks, depending on the nutrient load and carbon source used.  Colony densities can be adjusted by controlling the amount of the carbon sourced dosed.  When the bacterial colony is established, nitrates and phosphates can be controlled to very low levels or zero if desired.  Natural sea water contains 28ppm of carbon and may be present at this level in some of the better brands of salt mixes.  This may be the reason in part why aquarists who do weekly water changes experience healthier and algae free systems.  Carbon dosing is basically a means by which we dose organic carbon compounds.  These compounds include ethanol, acetic acid, sugars, bio-polymer pellets, and ascorbic acid.  When using a powder or liquid form of carbon dosing, it is important not to miss a dose as doing so will reduce the bacterial colony and will cause a set-back in developing the process.  Overdosing can also cause a dramatic drop in oxygen by an over abundance of bacteria which consume oxygen and can have a detrimental effect on the livestock in your aquarium.  It will also cause a large bacterial bloom resulting in cloudy water.  Should this happen, stop dosing immediately until the water clears.  At this point you will be basically starting over so do follow the manufacturer’s instructions to the letter.  Carbon dosing is beneficial in systems with a high bio-load where efficient protein skimming and frequent water changes are not enough to keep nitrates and phosphates at desirable levels.  Large systems or systems with a light bio-load that are efficiently skimmed will likely not benefit by this means if nitrates are already at acceptable levels.


Do I Need Additional Equipment to Dose Carbon

 Depending on the dosing method you choose, you may need nothing more than a syringe or measuring spoon.  The use of bio-polymer pellets will necessitate the use of a fluidized up flow reactor, flow control valve, and pump.  Regardless of the dosing method you choose, an absolute must is a good efficient protein skimmer rated for at least 1.5 times the volume of your tank.  Once the bacterial colony is established, they will consume nutrients and these nutrient laden bacteria will slough off or shear away from the biofilm the colonies produce.  These bacteria will need to be exported by a protein skimmer although the metabolism of these bacteria will also export some waste as nitrogen gas.


Types of Carbon Compounds

For this article I will concentrate on the most commonly used products for this purpose.  Before dosing any carbon source, test your system’s NO3 and PO4 levels.  Do not begin dosing without knowing this as this will be important later on to determine a maintenance dose level.  Good test kits are recommended and look for kits that are capable of accurately measuring low levels.



Carbon dosing initially started out with the use of Vodka as a carbon source.  Why Vodka you ask?  Since Vodka contains no additives and contains only water and the organic compound ethanol, it is much safer to use than other spirits which do contain additives that could have a negative effect on the system.  Vodka is also one of the more economical means of dosing providing you do not dose yourself with it while dosing the aquarium.  No need to buy high grade Vodka, the cheapest brand of 80 proof (40% alcohol) Vodka will work just fine. The following dosing procedure is recommended when using Vodka.

First three days – 0.1ml per 25 gallons of actual aquarium water.

Days four through seven – 0.2ml

Each subsequent week add an additional 0.5ml of vodka

After week two you should see a reduction of nutrients.  If no decrease is noted by your test results, increase the daily dose by another 0.5ml.

Once your NO3 and NO4 drop to an undectable or a level you desire, decrease the daily dose by one half.  It is at this point where you will need to determine a maintenance dose.  If nitrates and phosphates rise, increase the daily dose by 0.2ml.  If the levels remain undectable, decrease the daily dose by 0.2ml.  For reef systems we are looking for nitrate levels in the 5-10ppm range as some invertebrates such as clams do benefit by some nitrates present in the system.


Bio-polymer Pellets 

Two Little Fishies NPX Bioplastic Pellets

  An easier method of carbon dosing is by using bio-polymer pellets, sometimes called solid Vodka, solid polymers, and bioplastics.  These pellets or beads are made from petroleum based polymers. The heterotrophic bacteria live and feed on these pellets and in the process uptake dissolved nutrients from the water thus lowering nitrate and phosphate levels. The instructions that come with the pellets should state the amount required for a given tank size.  This method of dosing requires a fluidized up flow reactor, pump, and flow control valve.  Depending on the reactor chosen, you may have to purchase screens fine enough to prevent the pellets from escaping the reactor. Water flow is adjusted with the flow control so all the pellets tumble within the reactor.  This is important as too little water flow will cause the pellets to clump. The size of pump will be dependent on the size of the reactor, length of tubing from pump to reactor, and the amount of pellets required.

Reactors made for this application generally state the size of pump needed.  It’s much better to have too much pump as you can always throttle the flow back with the flow control. This method is much easier compared to the required daily dosing of Vodka.  The pellets will slowly dissolve in time and will need replenishment to maintain the desired bacteria population.  When the reactor is filled the first time with the recommended amount of pellets, it is a good idea to make a mark on the reactor showing the pellet level.  After a few months pass you can shut down the pump and observe the pellet level and refill as needed up to the line you originally marked when you first filled the reactor.  Much like the Vodka method, dosage (amount of pellets used) can be lowered or raised based on your nitrate/phosphate test results.  Like Vodka, overdosing pellets will cause the same problems, low oxygen levels and cloudy water due to an increase of bacteria.  It will take at least three weeks before an effective population of bacteria is present to begin reducing the nitrate/phosphate level in your system.  This method of carbon dosing seems to be the most popular at the time of this writing.


A fluidized up flow reactor is required to use biopolymer pellets.

There are many reputable brands of reactors on the market. 

A Two Little Fishies Reactor is shown above.  This reactor 

requires a set of screens for use with bio-polymer pellets.


A pair of Two Little Fishies reactor screens.  A template is provided

to cut the screens to the proper size depending on which model

TLF reactor you have purchased.


Reef Actif (Tropic Marin)

  Tropic Marin recently introduced a new product called Reef Actif which basically accomplishes the same function as the above without the need of a reactor and pump.  Reef Actif is dosed by mixing the recommended amount of the product with seawater.  One half teaspoon is the dose recommended to treat a 60 gallon tank weekly.  The product is economical to use and a 100ml container should last at least three months for the above size tank.  On larger (150+ gallons) systems it may be more economical to use the pellets with a reactor. 

 Reef Actif is a fine powder very similar to the consistency of flour.  Tropic Marin states that the polymers they use are naturally occurring marine polymers produced by sea weeds. When mixed with sea water, the product becomes suspended in the aquarium water where it bonds with both nutrients and other contaminants making them available as nutrients to heterotrophic bacteria and other animals that require dissolved organic material to survive.  These bonded nutrients are a source of beneficial bacterial nutrition for clams and some corals such as Acroporid and Pocilloporid corals.




                   100 and 500ml containers available         A 60 gallon weekly dose                            

 Reef Actif is also mixed in with Tropic Marin’s Bio Actif System Salt.  Using this salt would eliminate the use of Reef Actif or other carbon dosing products only if weekly water changes are performed.  If water changes are conducted bi-weekly, then Reef Actif would need to be dosed on off weeks.  This salt mix is not a bargain brand at $105.00 which is the average etailer price for a 200 gallon bucket

Users have reported excellent results with this product.



Tropic Marin Bio Actif System Salt

Liquid nutrient control products have hit the market by storm recently.  Although most are carbon based but there are a few that are bacterial based which perform their job as soon as they hit the water.

 Prodibio BioDigest



Although not exactly a carbon dosing product, the company states that BioDigest is made up of natural nitrifying, nitrate reducing and facultative bacterial strains selected for their ability to convert ammonia into nitrites, nitrites into nitrates and nitrates into nitrogen.  These bacteria work together with each strain of bacteria finishing up the work started by the others.  Some of these bacteria are capable of biosynthesizing nitrate reducing enzymes in aerobic conditions.  This in turn enables the water to be effectively purified, nitrates and phosphates to be reduced thereby preventing the spread of nuisance algae.

 One benefit of this product is that it is only necessary to dose every two weeks as there are enough bacteria present in each vial to provide effective results during this time period.

The product is available in 6, 12, and 30 vial boxes with an average etailer price of $17.99, $26.99, and $45.99.  One vial will dose a fifty gallon tank for two weeks.

Customer reviews of this product have been very favorable.


Brightwell Aquatics Reef BioFuel


Like Vodka, the main goal of using Reef BioFuel is to provide a source of non-alcohol based organic carbon to the heterotrophic bacteria which in turn feed on dissolved nutrients in the form of nitrate and phosphate.  In medium to high nutrient systems, a 5ml daily dose is required.  In low nutrient systems the dose can be cut in half.  Like similar products, nitrate and phosphate tests will need to be carried out to determine a maintenance dose. The product is available in 250ml, 500ml, 2L, and 20L containers.  A 500ml container will treat a fifty gallon tank for approximately 100 days and has an average etailer price of $13.49.  The cost may not be very economical when compared to a 1.75 liter bottle of inexpensive Vodka for about 10 dollars which gives you 1750 milliliters of an organic carbon source.  Dosing Vodka also requires a lower daily dose.


Advantages Of Carbon Dosing

 Lowers dissolved nutrient levels in the form of nitrates and phosphates.

Reduces or eliminates nuisance algae and Cyanobacteria growth.

Improved water quality and clarity, especially beneficial for sensitive fish such as Tangs and Butterflyfish.

Provides a food source in the form of bacterioplankton for filter feeders that feed on bacteria including clams, some species of corals and filter feeders.

Eliminates the need for using carbon or other nutrient removal media.



 Can cause cloudy water if overdosed, resulting in reduced oxygen levels which can be detrimental to the livestock in the system.

If using polymer pellets, an initial expense for a reactor, flow control valve, and pump will be required.

Can initially (rare) cause an outbreak of Cyanobacteria but this is reversed once sufficient numbers of heterotrophic bacteria are present to outcompete the Cyanobacteria for food in the form of dissolved nutrients.



 Although I have only covered a few of the many products available, I recommend doing your homework before purchasing, compare products and read user reviews. Carbon dosing can be a very effective and inexpensive means to lower nitrates and phosphates in your system as well as providing a food source for certain invertebrates.  It will also reduce, if not eliminate nuisance algae growth and Cyanobacteria blooms in your aquarium.  I have been carbon dosing with Tropic Marin Reef Actif for the last three months.  I chose this product because I do not have room for a reactor and associated equipment.   All rock remains free of algae other than coralline, and the water has a noticeable improvement in clarity.  Corals appear to have better color and expansion as will be seen with all carbon based products used for this purpose.  Carbon dosing may not work in every system.  It has been noted that certain enzymes need to be present in order for the bacteria to utilize the carbon source but this is a rare occurrence.  The alternative in this case would be to use the Prodibio BioDigest or a similar product that provides the necessary bacteria.  Regardless of the product used, it is recommended to perform regular nitrate and phosphate tests to determine an effective maintenance dose.

New Print and eBook on Amazon

Marine Aquarium Algae Control

by Robert (Bob) Fenner

Carbon Dosing Article   4/13/12
Hi Bob,
The carbon dosing article is also schedule to appear in the next issue of CMA.  If you wish, you can place this on WWM as well.  I believe we are weak in this subject at present.
Re: Carbon Dosing Article

Well done James. Again, I take it these are others, the manufacturers' image work, and that we're okay to run them. B
Re: Carbon Dosing Article
Thank you Bob.  Yes, I have approval from all to use their photos.
Would you like me to forward their emails to you?
Re Carbon Dosing Article   4/13/12

Thank you James... no need to, but you should hold on to for your records. B

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