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Can plants cause high nitrite.

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Sorry this is little on the long side.


I had a tank with a lot of plants and the nitrite levels were very high. Ammonia was at zero and the nitrate was at the lowest level. I did a big water change and the nitrite level dropped to zero. Ammonia and nitrate was zero. The next day, before I left for work I tested the ammonia,nitrite and nitrate levels and the nitrite was at 5ppm and the others were zero. I did another water change and set up a plastic container to put the plants in. My plan was to take out everything out so it was just fish in the tank. The tank with the fish has had the levels  at zero.  It has been almost two days and the tank with just plants nitrite levels are super high(around 10ppm or more). The ammonia is showing little(.25ppm).


   1. Can plants make the nitrite level super high?

   2. Could it be the fertilizer or to much light?

  3. Can the fertilizer cause a false reading?

  4. Has anyone have had this happen to them and if so, what did they do to fix it?


I cycled the tank with out fish for about 6 weeks. I do water change once a week and do a big water change once a month. I have stated using Thrive fertilizer and ThriveCaps. I didn’t have this issue with API root tabs and API fertilizer. Was thinking I should stop using Thrive.

My pH is between 7 and 8.

My KH is at 4.

My GH is at 7. 

My tank is 29 gallons. 


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Alright, let's work backwards a bit - nothing in your fertilizers should be introducing nitrite into the water, and the lighting might just cause an algae spike. 

So relevant information -

what was your process for the fishless cycle? what kinds of readings were you getting and what process did you use to add ammonia?

How are you testing the water (API kit, test strips?) and can you see if another test confirms that high reading?

How many fish did you add after the fishless cycle? How long has it been since you added said fish? (depending on how you cycled and then added fish it's possible there's a bigger bioload than the tank is prepared to accommodate)

If all else fails, what are the measurements of your tap water?

Just trying to get some ideas going, hopefully it clears up soon!


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I cycled the tank by during fish food and a Squeezed a dirty filter from a friends tank into the water. I use the API master test kit. I have used the test kit on my friends tank and there are no reading of nitrite. I have had the tank up and running since the 5th of February. The only thing I think of at this point is something killed of my colony of bacteria. I’m going to the store after work to buy some items to help. Thanks for the taking the time to post. 

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Plants themselves cannot produce nitrates unless there is a large amount of organic matter decaying. Look at the ingredients for your fertilizer a lot of them have nitrates in them and this raises the levels of nitrates in the aquarium. Also how many fish do you have? If the bioload is to much the beneficial bacteria to convert. Also how quickly did you add your fish to the aquarium? Was it all at once or spread out over a few weeks? If you add to many fish at once the beneficial bacteria cant keep up with all the amonia and nitrates produced

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The plants are not the cause of your high nitrite. Your tank is not cycled. You should not squeeze old filter media into the tank - you should at min squeeze it into your filter so the bacteria gets into your media or better place it in your media - still without food it will die. If you do a bit of searching the vast majority of the beneficial bacteria will be found in the filter sponge or media (depending on type of filter). Substrate has some but not nearly as dense - though you do have a lot more substrate. 


Thrive adds a bit of nitrate but NOT nitrite. If it added nitrite it would poison your fishes rather severely every time used. The most likely reason you don't measure ammonia is because you do not have something producing a measurable amount of ammonia. 


personally I think the best way (or easiest way) to cycle a tank is to find a sponge filter with live bacteria (any friends with cycled tanks?) and put it in your tank iwth a couple of fishes.

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