BIOLOGICAL FILTRATION IN AQUARIUMS AND PONDS

Biological filtration is the process whereby potentially toxic organic substances are removed from aquariums and ponds by various beneficial bacteria that utilize them as a natural food source. Small numbers of these bacteria will come into the aquarium and pond on the surface of the fish, through the air, or in the food. Bacteria can also be provided by introducing some gravel or filter material from a well established aquarium or pond which already has gone through the nitrogen sequence. A cubic inch of gravel or filter material per ten gallons of water is sufficient. Given an adequate food supply, oxygen and a suitable substrate, these bacteria will quickly spread throughout the new gravel and filter bed. They will typically establish themselves on the surface of the gravel, the inner surfaces of the aquarium or pond, inside filter tubing and anywhere else that has a water flow resulting in good oxygen levels.

Uneaten food, dead and decaying animals and plants, as well as the fecal, urinary and respiratory waste products of the animals are broken down into ammonia by heterotrophic bacteria in a process called ammonification. Also, a large part of the excretion of fishes is already in the form of ammonia. Within the restricted volume of an aquarium or pond, and in the absence of an established colony of bacteria, ammonia can increase quickly to toxic- even lethal- levels. Ammonia can place a high level of stress on many fishes, especially those that have been recently moved or handled. All efforts should be made to reduce these stress levels when possible. The use of a high quality test kit (such as Kordon's Ammonia Water Quality Test Kit) is extremely important at this stage of an aquarium's existence. High levels of ammonia (.5 or above) as indicated by your test kit can be easily treated with the use of AmQuel®, Kordon's patented ammonia removing water conditioner.

Following the ammonification part of the cycle, two groups of autotrophic nitrifying bacteria become established in sequence. The nitrifying bacteria, in a process called nitrification, use the ammonia as food, thereby eliminating it from the water. The first group of nitrifiers oxidize ammonia into nitrite. In a new tropical aquarium set up in which the bacteria of the nitrogen cycle are not in balance, the high ammonia level declines within an average of 1-2 weeks. Ammonia is replaced by a rising level of nitrites, typically within an average of 2-3 weeks. Nitrite is stressful and is toxic to freshwater fish and somewhat less toxic to marine animals. Its concentration in the aquarium or pond needs to be carefully monitored with a good quality test kit such as Kordon's AquaTru® Nitrite Test Kit. As the nitrite levels rise above .6 ppm (mgL), careful attention should be paid to the action of the fish. If any unusual behavior or stress is observed, immediate action should be taken to improve the situation. For fresh water fishes, the addition of salt to the water coupled with a partial water change, will often solve the problem. For marine fishes, a partial water change should be performed. Note the level of nitrite indicated on the test kit at the time of the problem and continue monitoring the nitrite levels, making changes as indicated by the readings.

The final stage in most home aquarium and ornamental pond situations is nitrate. Nitrate is considered nontoxic even at levels as high as 60 to 80 ppm (mgL) in freshwater and 10 to 20 ppm (mgL) in salt water. In aquariums and ponds containing invertebrates such as corals, anemones etc., nitrate levels can become more critical. Toxic levels for your particular aquarium situation can best be determined by careful monitoring of the nitrate levels and close observation of the aquarium residents. Levels as high or higher than these should be corrected by a water change. Nitrates can be removed naturally by a process called denitrification, but this is risky and best left to those with a high degree of skill and experience. For the rest of us, nitrate is removed by performing regular water changes. This actually accomplishes two things; the lowering of the nitrate level and the removal of other unwanted pollutants that are not as easily measured.

Using water quality test kits to monitor the progress of biological filtration.
Use a pH kit regularly to be sure that the acidity is not increasing. A drop in pH indicates that water conditions are worsening. Below a pH of 6.5 in fresh water, the bacteria associated with the nitrogen cycle will progressively cease to function, disrupting the cycle. When the cycle is disrupted, ammonia levels will rapidly increase. For additional details on pH, click here: pH TEST KITS

Use an ammonia test kit the first weeks in the cycle to monitor the nitrifying bacteria's progress. Monitoring the cycle will insure that, after the first week in tropical conditions (longer in colder water conditions), the ammonia is not reaching toxic levels, and after its peak is steadily declining and then disappearing. Check for ammonia at later intervals to be sure the cycle has not been disrupted. For additional details on ammonia, click here: AMMONIA INFO

In the second and later weeks use a nitrite test kit to be sure nitrite is not reaching toxic levels, is progressively declining and then disappears. A nitrite reading is an indication that the bacteria are becoming established and functioning. Use a nitrate test kit to monitor the rise in organics over the ensuing weeks and months. Do periodic water changes to lower nitrate levels.

Some Commonly Asked Questions Concerning the Nitrogen Cycle:
What about products that claim to speed up or eliminate the nitrogen cycle? Based on the independent scientific laboratory results we know about, we are skeptical of the claims. Firstly, the bacteria involved in marine conditions are entirely different than those for fresh water. The cultures of bacteria used in aquarium products are mostly from cultures originally developed for outdoor freshwater sewage disposal plants. Those bacteria are not expected to survive in salt water. Also, the requirements for aquarium and ornamental pond keeping are entirely different than sewage conditions. We have not seen it technically proven that the sewage bacteria colonies contain the kinds that will function in biological conditions for aquariums and ornamental ponds. Caveat emptor.

What about the use of Kordon's AmQuel in removing toxic ammonia? Will this interfere with biological filtration and the "nitrogen cycle"? In both fresh and salt water, AmQuel combines with the ammonia molecules, forming new molecules that are irreversibly nontoxic. The nitrifying bacteria utilize these new molecules as a food source just as they did the original ammonia molecules. AmQuel is the easiest way to totally eliminate toxic ammonia in the water without disrupting the nitrogen cycle. For additional information on this essential water conditioner, click here: AMQUEL

What else should I know about the differences in biological filtration between fresh and saltwater conditions? The bacteria are entirely different between fresh and salt water. Therefore, while the sequence of events in the nitrogen cycle are the same, the exact timing will vary and the tolerances are narrower in salt water. Also salt water provides lower oxygen levels than does fresh water. The bacteria associated with the nitrogen cycle need oxygen and will progressively cease to function at low oxygen levels. Natural sea water pH is 8.3 and lowering pH levels severely affects the metabolism of the nitrogen cycle bacteria. Saltwater conditions need to be monitored more accurately than for comparative freshwater conditions.