Natural Nitrate and Phosphate Control in Marine Aquariums – Part 1 – Carbon Dosing Basics

In the never ending fight against excess nutrients in the home aquarium, many products have come along in recent years to help aquarist win the battle.  Chief among the nutrients with which all aquarium owners struggle (especially the reef aquarium owner), are nitrates and phosphates.  These nutrients fuel algae growth, and in the case of nitrate, can jeopardize animal health as well.   In the reef aquarium, nitrates and phosphates are a serious problem, and controlling these nutrient levels are vital to the health of the living coral and invertebrates in these systems.

Phosphate absorption media, macroalgae refugiums, deep sand beds, and frequent water changes have been the methods used by most to maintain low nutrient levels in aquariums over the years.  More recently, aggressive biological methods for combating nitrates and phosphates have become increasingly popular, and several Carbon dosing methods to remove nitrates and phosphates have been developed.

So, what is Carbon Dosing?  First of all, for the folks who are completely new to the term, it has nothing to do with activated carbon, or charcoal, that you use in your aquarium filter.  Carbon Dosing is based on the theory (which is debated by some) that limited carbon availability hinders the growth of beneficial bacteria in the aquarium.

Carbon (C), Nitrogen (N), and Phosphorus (P) are basic elemental building blocks used by organisms, and in studying phytoplankton, scientists have discovered that these elements appear in their body tissues in a specific ratio: 116 C: 16 N: 1P (known as the Redfield Ratio). This Redfield Ratio of elements in phytoplankton is close to the ratio of the same elements in seawater.  It has been shown that if there is an excess of one or two of these elements, then the limiting factor in growth of phytoplankton must be the other element(s).  Bacteria, like phytoplankton, consume these elements for growth and reproduction in the aquarium (although not is a strict ratio). So an aquarist can assume that in the presence of excess Nitrate or Phosphate in the aquarium, Carbon must somehow be the limiting factor for consumption of these elements by the bacteria.

Carbon Dosing theory has been around for some time, but has gained in popularity in recent years, and the success that reefers have achieved using this method are undeniable.  Vodka (yes that vodka) has been the primary carbon source of choice, since it is cheap and readily available. Sugar and vinegar have also been used.  Carbon Dosing has been used primarily by the advanced reef aquarist, on SPS dominated reef systems, but it can be used in any situation.  By adding an available carbon source to the aquarium (such as the ethanol in vodka), the growth of beneficial bacteria is increased and in turn the amount of nitrate and phosphate that is bound in the tissue of these microbes is increased.  These microbes are then removed from the aquarium through protein skimming and mechanical filtration. Those who use the vodka dosing method report a dramatic increase in the amount and thickness in the skimmate produced from their protein skimmers, presumably from the increased bacteria and their organic laden by-products.  Once the beneficial bacteria population is established, it can be maintained by continued vodka dosing, and nitrate and phosphate levels stay at extremely low or even undetectable levels.  Maintaining this low nutrient system, improves the overall health of the system, eliminates nuisance algae, and promotes brilliant coloration in corals. Another benefit to this increased bacteria population, also referred to as bacterioplankton, is that it serves as a supplemental food source for corals and filter feeding invertebrates.  This highly efficient nutrient removal system, also allows the user to maintain an increased bioload and feeding regiment in their aquarium.

The downside to this method is that Vodka needs to be dosed daily, and dosage levels are largely achieved on a trial and error basis.  Overdosing vodka can result in unwanted cyanobacteria and algae growth, or in creating an environment that is “too clean” which can also affect the health of your corals.  Advancements in protein skimmer efficiency have boosted the success of carbon dosing, which most definitely has had an impact on its recent rise in popularity.  Advancement in commercially available carbon sources like Brightwell Aquatics Reef Bio Fuel, and Red Sea’s NO3:PO4-X have eliminated the need for Vodka and other sources of Carbon (and are also safer to keep around).  Beneficial bacteria blends that jump start and maintain the process like Brightwell Aquatics Microbacter 7, will help insure that the added carbon will go towards the growth of wanted bacteria, not nuisance algaes.

These are the basics of Carbon Dosing in the aquarium, check back for part two of this article in the near future, where I will discuss some advancements and new products that have hit the market.  If you have any questions or observations on carbon dosing, please share in the comments section.

Until Next Blog,

Dave