I am attempting a fishless cycle on a small, nano-planted tank that is getting stuck on extremely high levels of nitrite. The tank has been set up for about two weeks now.

I am not dosing ammonia. I have two nerite snails in the tank that are creating some waste, so I get my ammonia from that and they are controlling any algae that might happen. My ammonia levels are usually always around 0.25 ppm.

After a water change, the nitrite spikes within 24 hours and then the nitrate will spike about 24-48 hours after that. However, the nitrite is still at extremely high levels even after the nitrate spikes.

Is this a patience game, waiting for the good bacteria to build and catch up to the output of nitrites? I have heard to do a water change when the nitrates get too high, but I don't want to disrupt the nitrite level in possibly letting good bacteria to colonize.

Any help on this would be awesome!


  • You may want to consider switching to cleaner shrimp. THE problem with snails is that they produce a lot of waste, so your nitrate/nitrite problem is not uncommon. Also, sometimes the problem with persistent spikes is decaying matter rather than water quality.
    – rlb.usa
    Oct 13, 2016 at 16:46

2 Answers 2


Basically it is indeed a patience game.
But how often do you change the water, and how much? Since your doing a fishless cycle (which is indeed the recommened way to do it), you don't actually have to do water changes.
If you replace to much water, it's indeed possible that your cycling has to start all over again every time.
Just let it rest for about 3-4 weeks and then check the nitrite levels. By then they should already start decreasing/be zero.

You can also find more information in this answer: How does one effectively "cycle" an aquarium?

  • I do a 40-60% water change about every 2-3 days because the nitrates start to spike. Oct 11, 2016 at 16:53
  • I have live plants in the tank and I am worried the plants won't be enough to keep the nitrates down. Oct 11, 2016 at 16:57
  • Don't worry about the nitrates yet (in fact you should not worry much about that at all).Stop doing these water changes, and just wait another 2-3 weeks. By then I assume your nitrites will already be a lot less/zero. And then you can check if it's needed to do anything about the nitrates.
    – Diether
    Oct 12, 2016 at 7:51

It can take 4-6 weeks for your aquarium to cycle. So you just need to wait.

You don't need to do any water changes, this is only required when doing a cycle with fish so the ammonia/nitrite is kept low.

All you need to do is keep the ammonia up. Test your tank every day and if ammonia is below 2 ppm then top it up to 2 ppm. (you need to keep feeding the bacteria which is producing ammonia or they will die off)

Once ammonia/nitrites go to zero within 24 hours of being 2 ppm then you are cycled.

You just need to be patient.


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