If you have a relatively new tank, or if you’ve recently added fish to your aquarium, you may have noticed your nitrate levels increasing. While some nitrates are safe in an aquarium, it’s generally recommended to keep the level between 20-40ppm. High nitrates can be detrimental to fish in your tank and algae loves nitrate. If given the chance, algae will gobble up the nitrate in your tank and then hold on for dear life. Algae blooms can be difficult to get under control once they start to take over. So, what causes high nitrate levels, and how can you control them?divider1- goldfish

Causes of High Nitrates

  • Detritus: Detritus is the build-up of waste from the creatures living in the aquarium as well as the decaying bodies of any fish or invertebrates that may have died in the tank. If you have hitchhikers on plants or décor, you may end up with a decaying animal you didn’t even know you had, like pond snails and hydra.
  • Decaying Plants: This is like detritus, but the decaying parts of plants in your tank can increase the nitrates in your aquarium. This includes leaves that have dropped from plants that are allowed to stay in the tank and rot instead of being removed.
  • Overfeeding: Overfeeding poses two problems. The first is that it increases waste from tank residents. The more they eat, the more they excrete. The second problem is that overfeeding may lead to food being missed, which will then rot, adding to the nitrates in the tank. In fact, allowing food to rot in a tank is one of the ways to perform a fishless tank cycle because it increases waste products in the water, encouraging the growth of nitrifying bacteria.
  • Overstocking: Overstocking your tank is similar to overfeeding. You’re just increasing the amount of waste in the tank and if you aren’t managing your overstocked tank well, you will end up with a buildup of waste products.
  • Dirty Filters: Dirty filters may not reduce waste products and grow bacteria as they should be. Generally, the recommendation is not to change your filters out since they are the main source of good bacteria in your tank. However, your filters do need to be rinsed or gently squeezed out in dirty tank water every few water changes to maintain efficacy.
  • Tap Water: Some tap water has nitrate already in it, so you may be adding nitrate to your tank inadvertently during water changes.
water testing strip

Image Credit: Dmitri Ma, Shutterstock

Ways to Lower Nitrates

  1. Decrease feeding: If you reduce the amount of food per feeding or the number of feedings per day, you will have less food waste producing nitrate in your tank. If you have the tank space, consider adding in fish or invertebrates that will help clean up food from the tank floor, like dojo loaches and mystery snails.
  2. Decrease your number of tank residents: If you are keeping an overstocked tank and aren’t interested in more frequent water changes, consider decreasing how many fish you’re keeping in your tank. You can start a second tank and move some residents there once it is cycled or you can give some fish away. Local fish stores will often take fish you no longer have space for.
  3. Water changes: Water changes are a great way to quickly reduce nitrates, as well as other toxins in the tank. Evaluate how frequently you are changing your tank water and how much water you are changing out at a time. Depending on your tank, you may need to perform water changes multiple times per week, but you may also be able to do weekly, bi-weekly, or even monthly water changes.
  4. Plants: Plants LOVE nitrate! This is a great nutrient for many plants, so adding plants to your tank is probably the most efficient and beneficial way to remove nitrate from your aquarium. Plants will absorb the nitrate, as well as other things that are toxic to fish, and release oxygen into the water, improving the water quality in your tank. Duckweed, moneywort, water wisteria, and water sprite are all great options for removing nitrate in freshwater tanks.
  5. Bacteria: Quick start or cleaning bacteria may help establish or re-establish the biological filtration in your aquarium. Good bacteria are necessary for a healthy tank and will help reduce toxic levels of chemicals in your aquarium.
  6. Nitrate reducing chemicals: If you’re having trouble controlling the nitrate levels in your aquarium and have tried the things above, there are products you can purchase to add to your tank water to help bind to and eliminate the nitrate in your tank. Seachem Denitrate is a great product for this option. These products are made to help control nitrate levels once they are already being lowered by other means, so don’t expect a quick fix with these.

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In Conclusion

If you aren’t sure about nitrate levels in your tank but are struggling with algae blooms, then an aquarium test strip kit is a good option for you to see where the nitrate levels stand in your freshwater aquarium, as well as other things like pH and ammonia. These kits are also available in saltwater, reef, and pond options. Using kits like this will help you determine if your tank is properly cycled and it will give you a good idea of whether or not your tank is overstocked or your filtration is inadequate. Keeping nitrate levels under control in your tank will save you a lot of grief from fighting algae blooms.


Featured image credit: Suthiporn Hanchana, Shutterstock