Preferences of Nitrifying Bacteria

Nitrifying bacteria are beneficial microorganisms that drive the nitrogen cycle in natural aquatic ecosystems and the small self-contained ecosystem of an aquarium. They establish themselves on various surfaces in the aquarium to function as a biological filter, converting toxic ammonia to nitrite, then nitrite to less toxic nitrate. Like any living organism, they have specific environmental preferences that affect how well they grow and perform. In this article we cover those preferences — including temperature, pH, dissolved oxygen, salinity, and the effects of common chemicals — so you can create the best possible conditions for your biofilter.

Products like FritzZyme® 7 and TurboStart® 700 for freshwater, FritzZyme® 9 and TurboStart® 900 for saltwater, introduce concentrated cultures of live nitrifying bacteria to establish or restore that biological filter quickly.

Medication & nitrifying bacteria

Nitrifying bacteria are gram-negative rods up to 2 microns long. Unlike pathogens, nitrifiers are non-pathogenic and beneficial — but because most antibiotics target gram-negative bacteria broadly, they affect nitrifiers and pathogens equally. Other inhibitory chemicals include formalin, formaldehyde, chlorine, chloramine, malachite green, methylene blue, acriflavine, household disinfectants, copper (at 0.20 mg/L or higher), potassium permanganate, and chloroquine. Always perform a 30% water change and add fresh activated carbon after using any of these chemicals to remove residual byproducts. Then reintroduce nitrifying bacteria to restore the biofilter.

Chemical ammonia removers & nitrifiers

Ammonia removers must be evaluated carefully since different formulations pose different risks. Avoid any containing formalin — whether cycling or not. Formalin (a form of formaldehyde) inhibits nitrifiers already established in the filter, as well as those in bottled bacterial products. Many ammonia removers also drop pH; others introduce phosphates. If your tap water contains chloramine, use FritzGuard® followed immediately by Fritz A.C.C.R. to address the ammonia left behind.

UV sterilizers, protein skimmers & ozone generators

Nitrifiers prefer to attach to filter surfaces after the initial inoculation period, which takes approximately five days under optimal conditions. Until attached, the bacteria are vulnerable to removal by mechanical and chemical filtration equipment. Turn off UV sterilizers, ozone generators, and protein skimmers, and remove sub-micron mechanical filter media (5 microns or less) before adding bacteria. Wait five days before turning them back on.

Temperature & salinity

Cycling within the optimal temperature range of 77–86°F produces the best results. Cold water tanks should be lowered slowly over several days after cycling is complete. If a system cannot be cycled within this range, use double the standard dosage and expect the process to take longer. Nitrobacter/Nitrococcus are more sensitive to low temperatures, making nitrite problems more likely in cold water tanks. Freshwater nitrifiers tolerate salinities of 0–20 ppt, while saltwater nitrifiers prefer 20–44 ppt.

pH and alkalinity

Due to differences in pH preferences, fresh and saltwater systems tend to accumulate different compounds during cycling — marine hobbyists should watch nitrite levels closely, while freshwater hobbyists should monitor ammonia. pH stability is critical for nitrifying bacteria. The nitrification process consumes bicarbonates and produces carbon dioxide, which lowers pH over time. If alkalinity is initially low, pH swings can be significant. Starting bicarbonate levels of 100–200 mg/L are recommended.

Dissolved oxygen

Nitrification stops below 2–3 mg/L of dissolved oxygen (DO). Complete oxidation of ammonia requires 4.57 mg of oxygen per 1 mg of ammonia. For best results, DO levels should be above 80% saturation — at least 6 mg/L. Nitrobacter/Nitrococcus are particularly sensitive to low DO; nitrite problems typically follow when levels drop. Biofilters can accumulate sludge over time, restricting flow through parts of the filter — a condition called channeling. Channeling promotes anaerobic bacteria, produces toxic compounds, and inhibits nitrifiers. Regular addition of heterotrophic bacteria, such as those found in FritzZyme® TurboClean, helps eliminate sludge and prevent anaerobic pockets in both the filter and substrate.

Odor and appearance

Nitrifying bacteria cultures have a slightly earthy smell and range from rosy to dark brown in color. Color and odor vary slightly between batches and are not indicators of viability. Each batch is individually tested and must pass quality control before shipping. Always use before the expiration date printed on the bottle.