I performed a water change two days ago. My ammonia levels were at 0.25-0.5 ppm right after the water change, which one user suggested was due to the chloramine removers.

However, it has been two days and I saw one of my fish lying at the bottom of the tank, resting... during daylight. Its back fin is also tense, as in, it's not as big as it should be because he's contracting it out of stress. I tested for ammonia and it's at 0.5 ppm. My nitrates have increased to 10 ppm. I'm going to perform another 25% water change.

I added a carbon filter two days ago inside my AquaClear filter consisting of a one-month old bio-filter and a mechanical filter. WHY IS THIS NOT WORKING?

EDIT Just performed another water change, it definitely has to do with the de-chloramines. Maybe they aren't settled? What is the chemical reaction behind it?

  • 1
    If you are concerned its the tap water, do your next water change with inexpensive spring water. If the ammonia spikes again, you'll then know its not the chloramines in the tap water causing the readings. Nov 29, 2013 at 4:58
  • 2
    Bring a sample of your aquarium water and tap water to a reliable aquarium shop for testing, along with the chemicals/treatments you are using. If routine maintenance is having longer-term unexpected results on your fish, it's not worth guessing and repeating the same course of treatment. Dec 2, 2013 at 15:50

2 Answers 2


If I were to make a safe guess, it would be the tank cycle is not completed yet. If it is a matured tank, then something must have been disturbed which triggered the tank cycle to reset. If your tap water has high chlorine/chloramines, this could possibly kill the beneficial bacteria colony inside the filter. If you have washed your filter using tap water, this might kill the bacterias a well. I am not sure if you're using any dechlorinator, if not get one. You could also try doing water changes using aged water. In that case age the water in a bucket for at least 24 hours with an added air-stone.

  • Sorry, but my tank completed its cycle two weeks ago.
    – Don Larynx
    Nov 28, 2013 at 7:46
  • 3
    I explained a few cases which might reset your tank cycle causing it to cycle again. Are any of those applicable for you? Nov 28, 2013 at 8:11
  • No, I do use a de-chlorinator as stated in OP.
    – Don Larynx
    Dec 2, 2013 at 19:34

Your tank must have too many fish. If you want fish Then you must understand the nitrogen cycle. The tank must cycle. That means the bacteria that break down ammonia into nitrate must be present. And you need plants. Those will use the nitrates for food.

If you have no plants. Then the nitrates will build up until they harm the fish. Once you do a water change some of the nitrates will be removed. This also removes the beneficial bacteria. And if you do a large enough water change and feed them too much too fast or have too many fish the ammonia will build up faster than the bacteria can deal with it. Once the bacteria return to normal they will convert the ammonia to nitrite then to nitrate and then it will start building up rapidly again without the plants.

It's a circle. An ecosystem in a fish tank. THe fish provide ammonia for the bacteria. And the bacteria and the light provide the food for the plants. Both plants and bacteria help keep the water clean.

In the absence of any plants algae will start to grow really fast because of the high level of nitrates. If you add plants and they keep the nitrates low you will also have lower algae growth.

  • If you already see nitrates then the bacteria is already present. So don't buy any kind of bacteria starter. That bacteria is so prevalent that you almost never need to do anything like that. Lower the amount of food you are feeding. And add plants.
    – Graig
    Aug 8, 2016 at 19:30
  • I already had plants.
    – Don Larynx
    Aug 16, 2016 at 18:55

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