Biological Filtration and Aquarium Health Maintenance - Page 2
Karl F. Ehrlich, Ph.D. and Marie-Claude Cantin Ph.D.
Copyright © 1995

Hardness is a measure of the calcium and magnesium in fresh water. Soluble calcium and magnesium can react with soluble phosphorous to form insoluble salts, which are not biologically active. Regions with soft water will have a greater need for additions of alkalinity and trace elements to maintain a healthy aquarium.

Trace Elements
Trace elements are required in small amounts by all living creatures. The elements can vary from sulfur for proteins, to iron for hemoglobin, to cobalt for vitamin B, to boron to a wide range of other elements. Lack of essential trace elements causes many diseases and can stunt growth. The same is true for the community of animals, plants and microbes in an aquarium. People take vitamin and mineral supplements to assure the presence of essential trace elements. Similarly, the use of Cycle Micro-Nutrient Formula assures the presence of essential trace elements for the microbes, fish and plants in the aquarium ecosystem.

The Microbial Team for Water Purification

Efficient water purification is dependent upon the presence and activity of balanced communities of water purifying microorganisms working together. It has been demonstrated even in natural environments, such as lakes, not only that bacterial populations change quantitatively and qualitatively both temporally and spatially within a lake but that the enzymatic activity and availability, which are critical to decomposition, also fluctuate widely. The lack of optimal water purifying communities and conditions is why sedimentation of organic matter often exceeds decomposition in lakes and why lakes age and become polluted. Heavy feeding as in aquaculture or a poorly managed aquarium accelerates the degradation of the water quality and the proliferation of diseases. All bacteria are obviously not the same, and all essential strains are not always present when needed. This explains why total bacterial counts do not give an adequate indication of bacterial purification efficiency. It is essential that all necessary strains of the team of water purifying bacteria always be present if one wishes to achieve consistent and more complete water purification.

Life as we know it is based on molecules containing carbon. Living creatures can be divided into two major groups according to the type of carbon that they use for food: organic and inorganic.

Heterotrophs - use organic carbon. This can range from proteins and fats to simple sugars. Heterotrophs range from bacteria, which digest sludge and fish wastes, to higher life forms such as people. Bacteria are very simple creatures. Some produce enzymes to solubilize fats. Others produce enzymes to solubilize proteins. Still others are required to solubilize carbohydrates or cellulose. Many strains do not synthesize enzymes for solubilization of solids; these bacteria grow on products solubilized by others. Cycle Sludge Removers provide a balanced community of heterotrophs selected for their synergistic ability to improve water quality.

Lithotrophs - use inorganic carbon. This group includes plants, which incorporate carbon dioxide. Nitrifying bacteria are also lithotrophs, which incorporate bicarbonate and convert it into cellular proteins and fats. Cycle Biological Supplement provides bacteria for efficient nitrification.

The Microbiology of Aquarium Health Maintenance

There are four principal phases of bacterial water purification: solubilization of solids, removal of dissolved organic matter (carbonaceous BOD), nitrification and denitrification. (Figure 5) (Erlich et al., 1991) Each of these processes requires specific conditions, some of which exclude the simultaneous occurrence of the other processes. Understanding requirements for each of the processes is the first step in controlling them.

Solubilization of Solids

Bacteria can only use soluble food, which is able to pass through their cell wall. Enzymes are produced by bacteria to solubilize solids. Solubilization of solids produces carbonaceous BOD, soluble phosphorous and/or ammonia depending on the nature of the solids. The carbonaceous BOD may include fatty acids from breakdown of fats and amino acids from the breakdown of proteins. Production from these organic acids, as for the acid generated by nitrification,may require pH adjustment. Balanced communities of water purifying bacteria, such as are found in Cycle Biological Supplement and Cycle Sludge Removers are required to assure that the by-products of sludge solubilization are rapidly removed.

Removal of Carbonaceous BOD

Bacteria can be divided into two groups based on their feeding ecology: heterotrophs and lithotrophs. Heterotrophs use solubilized organic sources of carbon from proteins, fats and carbohydrates to build their body components. Lithotrophs use inorganic carbon (carbon dioxide / carbonate) for the same purpose. Removal of carbonaceous BOD is accomplished by heterotrophic bacteria. Nitrification is a function of lithotrophic bacteria. Removal of carbonaceous BOD results in production of bacterial biomass, carbon dioxide, water and insolubilization of phosphorous as it is incorporate into cells. Bacterial water purification results in a net reduction of approximately 60% of the organic carbon due to respiration and conversion to CO2. THis is also the end product of sludge biodegrations.


Nitrification not only converts ammonia via nitrite to nitrate but also reduces soluble phosphorous due to cellular incorporation (Figure 5). Nitrification requires the presence of oxygen as well as a source of inorganic carbon. Removal of dissolved organic material (carbonaceous BOD) by heterotrophic bacteria is a precursor to nitrification. High levels of soluble organic products can inhibit nitrification. Nitrate synthesis generally occurs when soluble carbonaceous BOD is below 20 mg / L.

The main concern of biological filtration in aquaria is control of ammonia and nitrite. Nitrosomonas transforms ammonia into nitrite, which is then converted to nitrate by nitrobacter. The general chemical pathways are described below.

NH4+ + HCO3- + O2 + Phosphorous + trace elements->bacterial biomass + NO2- + H+(acid)

NO2- + HCO3- + O2 + Phosphorous + trace elements->bacterial biomass + NO3

There are several noteworthy points in the above relationships, which may explain why rates of nitrification vary.


Denitrification results in the removal of nitrogen from the water by conversion of nitrate into nitrogen gas, which enters the air. Denitrification generally requires anoxic conditions and adequate soluble organic carbon. This combination of conditions is usually lacking in an aquarium, and this prevents the complete removal of nitrate.