I have the following tanks:

  • 5 gallon, 2 months old - housed betta and shrimp
  • 10 gallon, 2 weeks old - used established media to seed aquarium alongside cycle and beneficial bacteria
  • 3.5 gallon - currently seeding with established media

For the 3.5 gallon, I understand the 0 reading on nitrates, but not on both of my other tanks. (0 nitrites, 7 pH, heated to 78 °F / 26 °C), the rest is neutral on my tests or in the right parameters.)

Why do my nitrate readings always come out as 0?

I do weekly water changes at 30% with dechlorinator and add beneficial bacteria every other week. In addition, I vacuum gravel every other change. I've had no ammonia spikes, no dying fish, no cloudiness.

Why do my nitrates stay at 0?

  • 1
    what type of water test do you use the liquid test kits are often more reliable than the test strips can be.have you tried to add amonia in your tank to force a reading on the test you use.you do not need to change water every week while you cycle your tank it is better to wait until you get a reading of your test and then start the water changes. Commented Feb 16, 2019 at 6:47
  • 1
    The tank has mature bacteria that breakdown any urea; An objective of developing a balanced aquarium. Commented Feb 18, 2019 at 21:17
  • If you are doing the liquid aquarium test kit - make sure to follow directions. Specifically, about shaking bottle #2 for 30 seconds, them waiting for a few minutes for color to develop... Nitrate test is not as immediate as others. Commented Feb 20, 2020 at 5:20
  • Take samples of your water to your local Petco and they can test it for you. just mark the samples so you know what tank they came from. Commented Dec 13, 2020 at 14:50

1 Answer 1


Nitrates are the the not-so-toxic part of the nitrogen cycle.

The decomposition of fish waste goes like this: Ammonia -> Nitrite -> Nitrate, with the two transitions needing a different bacteria.

Maybe the bacteria that decomposes Nitrite into Nitrate is not present in sufficient numbers in your aquarium. In this case you would observe a presence of Nitrites.

Maybe your Nitrates are all eaten up by some live plants if you have any. The other way to get rid of Nitrate is through water changes.

A reading of 0 Nitrate means either the tank is extremely clean, or completely without a functional cycle. Or maybe a tank without any live animals. If you want a cycle you need someone pooing in there. If you don't have build-up of the toxic ones, Nitrite and Ammonia, you should not worry too much.

Keep doing regular water changes they are very important anyway. You could do smaller, more often also, which is more safe. Never completely clean the substrate or the filter media.

Can you detail what are the "beneficial bacteria" that you add? I would recommend letting them make a population naturally.

2 weeks is also very young for a tank so it's possible the cycle is not yet stable. The 2 months old should definitely have something in it. If not Nitrate, then nitrite. If not nitrite, then ammonia should be present. Consider that your test-kit might be defective, try another one.

Bit of unasked-for advice: Betta would be a lot more happy, active and colorful in the 10 gal. Everything under 10 gal is extremely small, I would only approve it for shrimps or snails. Not even sure what's the point of a 3.5 lol.

Wish you to have fun with your aquariums !

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