7 Tips to Fix Ammonia and Nitrite Spike in a Fish Aquarium

Even for a well cycled home aquarium, sometimes out of blue you get a reading of ammonia or/and nitrite. When such incident has happened, we call it ammonia and nitrite spike, or a mini-cycle. We must fix the problem as quickly as possible in order to prevent fish from getting killed. To fix the problem, we must first determine the causes for the build-up of ammonia and nitrite.

Ammonia (NH3) and nitrite (NO2) are toxic to aquarium fish even with the lowest concentration. As fish keepers, we must keep both of them at zero in the aquariums all the time in order to keep fish alive. While most fish might not just drop dead on the first sign of low concentration of ammonia and nitrite, they will be permanently damaged if the problem is not getting fixed soon.

What are ammonia and nitrite? Why are they in the fish tank?

Ammonia is a waste released by the aquarium fish. Not only do the fish constantly produce ammonia through their gills, but the fish poop and leftover fish food will also break down and produce more ammonia. In other words, it is impossible to stop the continuous production of ammonia in a fish aquarium as long as there is fish. Nitrite is a temporary product of aquarium nitrogen cycle, when some of the good bacteria in the aquarium system attempt to break down ammonia and turn it to nitrate. While nitrate is harmless at low concentration, nitrite is even more deadly than ammonia to the aquarium fish.

For more details, please refer to Aquarium Nitrogen Cycle and Fishless Cycling. In a well cycled aquarium, both the ammonia and nitrite readings should be 0ppm. If you have not done a fishless cycling before getting any fish, it is unavoidable to have high concentration of ammonia and nitrite in your aquarium once you have put fish in it. Read for more information on fishless cycling if you have no idea what it is.

Possible causes for ammonia and nitrite spikes in a cycled aquarium

An ammonia and nitrite spike in a well cycled aquarium can only mean one of the two things:
A. Bacteria colonies in your filter media have collapsed or at least being damaged.
This can happen when you have used some strong medications for your fish. Or perhaps you have washed the filter media too “clean” by using untreated tap water or squeezed it too hard and too many times. When you have fewer bacteria doing their job of converting ammonia and nitrite to nitrate, it is easy to understand why there is a surplus of ammonia and nitrite in the fish tank.

B. There is an increase in ammonia production in the fish tank.
Either you have overstocked the aquarium with too many fish (More fish mean more ammonia is produced), or there is something rotting in the fish tank. It could be too much fish poop or leftover fish food, or even one or two dead fish.

How to deal with ammonia and nitrite spike in an aquarium?

1. Reduce the ammonia and nitrite concentration by doing partial water changes
Short-term immediate quick fix is to do partial water changes. A 50% water change will decrease the ammonia and nitrite concentration by half. Likewise, a 75% water change will lower them to only 25% of the original concentration. You may do partial water changes multiple times in a row to reduce the toxic to a minimal level. Make sure you never do a 100% water change or anything close to it in order to avoid shocking the fish.

2. Make ammonia and nitrite temporarily harmless
Some aquarium water conditioners can make the ammonia and nitrite less harmful or even completely harmless for a certain period of time.
For example:
SeaChem Prime can temporarily detoxify ammonia by turning it to ammonium for up to 48 hours.
Kordon NovAqua+ can reduce the intake of nitrite for fish. If you use any of these water conditioners for every partial water change, you can reduce the damage of ammonia and nitrite to your fish.

3. Remove organic waste in the fish tank to reduce the ammonia production
All of these partial water changes are temporarily fix to lower the toxic, but not to eliminate its production. If you do not go for the source problem, the ammonia and nitrite will just build up again. That is why you must check your aquarium for any dead fish or other rotting organic matters. You may remove the dead fish by using a fish net. The removal of all the fish poop, leftover fish food, and other organic debris at the bottom of the fish tank can be done by using an aquarium vacuum. You can do the vacuuming at the same time you do a partial water change.

4. Feed the fish less to reduce ammonia production
Overfeeding is the #1 cause for water pollution in the fish aquariums. Under normal circumstances, you only need to feed the fish as little food as they can finish within 30 seconds. You must not see any leftover fish food after every feeding. In case of an ammonia and nitrite spike, you might want to reduce the amount of fish food your fish are getting whether or not you have been overfeeding. The less food you feed the fish, the less poop they will produce. You may do it by either cutting the portion of every meal, or feed the fish every other day instead of every day, or skip a few days of feeding in a row until the mini-cycle is over. Fish will be fine with no food at all for weeks.

5. Reduce the number of fish (or get a bigger fish tank and more efficient aquarium filter)
If the ammonia and nitrite spike is caused by too many fish in the aquarium, you must either reduce the quantity of fish in the fish tank, or you have to get a bigger fish tank with a more efficient aquarium filter if you want a long-term fix. You may also add a second filter to the existing fish tank to increase the biological filtration.

6. Fix the bacteria colonies in your filter media by having the aquarium fully cycled again
The good bacteria which feed on ammonia and nitrite prefer warmer water and more oxygen. They will multiply faster in a more comfortable environment. Just like when you do a fishless cycling, you can speed the process up by setting the aquarium heater higher to increase the water temperature to 86F+. You may also increase the water surface movement by adding more air stones to give the aquarium water more oxygen.

7. Use a live bacteria product to jump start/finish the aquarium nitrogen cycle
Fixing a mini-cycle in an aquarium with fish is the same as “fish-in cycling”. If you are willing to pay to fix the problem, the quickest way to restore the bacteria colonies in your filter media is to get a bottle of live bacteria product such as Tetra SafeStart. Get a bottle that is rated at least twice your fish tank size will fasten the cycling in the aquarium.

Sometimes a mini cycle might hit your aquarium unexpectedly. The above tips will help you solve the problem while minimizing the potential damage your fish might suffer from the toxic ammonia and nitrite. The same tips can also apply to those who skipped fishless cycling and later found the aquarium in the situation of ammonia and nitrite spike. If anyone has anything to add, please feel free to leave a comment.

Related Posts


4 thoughts on “7 Tips to Fix Ammonia and Nitrite Spike in a Fish Aquarium

    • Hi Umang,
      You may use Tetra SafeStart while the fish are still in there. They will not be affected. It is (good) live bacteria after all. Dump the whole bottle in. Once it is unsealed, it does not last long.

Leave a Reply

Your email address will not be published. Required fields are marked *


*