When it comes to keeping an aquarium healthy, maintaining proper water parameters is essential. Two of the most important water parameters to monitor are ammonia and nitrite levels. High levels of either can quickly become toxic to fish. While ammonia enters the aquarium through fish waste, uneaten food, and decomposing organic matter, nitrites are produced when ammonia is converted by beneficial bacteria through the nitrogen cycle. When nitrite levels climb too high in an aquarium, a water change is often recommended to help dilute the concentration. But does a water change actually lower nitrite levels directly? Or does it help in other ways? Let’s take a closer look.
How Do Water Changes Affect Nitrites?
When aquarists perform routine water changes, the goal is to lower nitrate, phosphate, and other dissolved organic compound levels that can accumulate over time. However, water changes don’t directly lower nitrite levels in the tank. This is because nitrites themselves are not removed from the water column during a water change. The main ways water changes help control nitrites are by:
- Diluting nitrite concentrations – Replacing some of the water will dilute nitrite levels to some degree. This helps prevent a rapid spike in nitrites.
- Removing organic waste – By siphoning debris from the gravel, uneaten food, and fish waste (which produces ammonia) are removed.
- Providing cleaner water – Chlorine/chloramines are neutralized and fresh minerals are added with conditioned new water.
- Aerating the tank – Water changes oxygenate the tank which benefits the nitrifying bacteria.
The nitrogen cycle bacteria responsible for the conversion of ammonia into nitrite (and eventually into nitrate) are not housed in the water itself. These beneficial bacteria colonize surfaces in the filter and substrate. Performing a water change does not directly affect their populations. While water changes are still extremely important for reducing nitrate and replenishing minerals, decreasing nitrites relies more heavily on allowing enough time for the nitrogen cycle bacteria to build up properly.
How to Lower Nitrite Levels
Since water changes do not directly remove nitrite compounds, the best ways to lower nitrite levels are to:
- Allow time for bacteria levels to increase – In new tanks, nitrites can accumulate before enough bacteria grow to convert nitrites into nitrates. Be patient and avoid overstocking during tank cycling.
- Reduce bioload – Don’t overfeed and house only appropriate numbers of fish. Overfeeding leads to more ammonia.
- Improve biological filtration – Use a quality filter and filter media like porous rock or ceramic rings. More surface area means more bacteria.
- Perform partial water changes – While not removing nitrites directly, water changes are still important to maintain clean water conditions.
- Use live plants – Plant growth can help uptake some nitrates. Floating plants are especially helpful.
- Use products with nitrifying bacteria – Bottled supplements like Tetra SafeStart can help jump start the nitrogen cycle.
- Use a chemical filter media – Carbon or specialty resins can help absorb and remove some nitrites from the water.
- Use air stones – Surface agitation improves oxygen levels which benefits nitrifying bacteria.
How Do You Know When Nitrites Are Too High?
Ideally, nitrite levels should be undetectable in a healthy, established aquarium. In new tanks, some nitrites may accumulate as bacteria populations grow. Here are some signs that nitrites are too high:
- Test kit readings above 0.25 ppm nitrites
- Fish gasping at surface
- Lethargic or stressed fish behavior
- Loss of appetite in fish
- Gas bubble disease
- Reduced gill function
- Rapid gill movement
Nitrite poisoning can be acute or long-term. Even small amounts above 0.25 ppm can take a toll on fish health over time. Act quickly if nitrite readings are continuously above 0 ppm.
Safe Nitrite Levels By Species
| Fish Species | Safe Nitrite Level |
|---|---|
| Bettas | Less than 0.5 ppm |
| Neon Tetras | Less than 0.2 ppm |
| Discus | 0 ppm |
| African Cichlids | Less than 0.25 ppm |
| Goldfish | Less than 0.2 ppm |
| Shrimp | 0 ppm |
Some species are more sensitive to nitrite levels than others. Know the particular tolerances for the fish you are keeping.
Using Seachem Prime to Bind Nitrites
While water changes don’t directly remove nitrite compounds, some aquarists use water conditioners like Seachem Prime to bind up free nitrites. When added to new water at water changes, Prime utilizes sodium sulfite to render both ammonia and nitrites non-toxic but still testable with kits. The bond lasts around 24-48 hours for nitrites. This can provide a bit more time for nitrifying bacteria to convert the nitrites into nitrates. However, it does not eliminate nitrites completely from the root cause. It’s best used in conjunction with the other methods described.
Best Filters For Nitrite Control
Filter selection plays an important role in promoting the growth of nitrifying bacteria. Here are some top filters to help control nitrites:
Canister Filters
- Fluval FX6
- Penn Plax Cascade
- SunSun HW-704B
- Marineland Magniflow
Hang-on-Back Filters
- AquaClear Power Filter
- Marineland Penguin
- Seachem Tidal
- Aqueon Quietflow
Sponge Filters
- XY-2831
- Aquaneat Bio Sponge
- Huijukon Double Sponge
Canister filters and sponge filters provide abundant surfaces for nitrifying bacteria growth. Models with flow control help avoid blowing bacteria off filter media.
Maintaining Proper Biological Filtration
Providing adequate biological filtration is imperative for controlling nitrite levels. Here are some tips:
- Avoid replacing filter media too frequently
- Use filtration sized for tank size and stocking levels
- Use coarse, porous media like sponges, ceramic rings, and bio-balls
- Supplement with mesh bags of biomedia placed in the filter or sump
- Consider a sponge pre-filter on the intake tube
- Rinse filter media in old tank water rather than tap water
- Add supplemental air stones near the filter outlet
Aim to maintain nitrifying bacteria colonies long term without disruption for ideal biological filtration.
Conclusion
In summary, performing frequent partial water changes does not directly decrease nitrite concentrations in an aquarium. While water changes are still vital for reducing nitrates, phosphates, and organic waste, lowering nitrites relies more on allowing enough time for bacterial levels to increase, avoiding overstocking, improving filtration, reducing bioload, and using live plants. Test kits, along with observing fish behavior and symptoms, help monitor nitrite levels. Aim to keep nitrites below 0.25 ppm or fully undetectable for long term fish health. Be proactive if levels start to climb in a cycled established tank.