The Dangers of High Ammonia, Nitrite and Nitrate - Rate My Fish Tank

What would cause high levels of nitrite if there are no fish in my tank yet
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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.
We have had a new 48L tank running, with no fish in it for three weeks and have high nitrite levels
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Every couple of days, do a 10%-15% , and after about a week,take a sample of your water to a fish store to get it tested. Most will test fresh water for a minimalfee, or even for free! If the store you got the fish from won't, checkto see if there is another local store that will. At this point, yourwater should test with high ammonia and maybe a trace of nitrite. Ifit isn't, don't worry. Just give the tank time. The cyclingprocess usually takes six to eight weeks. Nitrite can suffocate your fish, therefore you really don't want it in your tank
Photo provided by FlickrFish Tank Chemistry: Ammonia, Nitrate, Nitrite - YouTube
Photo provided by FlickrDetection of Nitrates and Nitrites in Fish Tank Water by Brianna ..
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The desired species of nitrifying bacteria are present everywhere(e.g., in the air). Therefore, once you have an ammonia source in yourtank, it's only a matter of time before the desired bacteria establisha colony in your filter bed. The most common way to do this is toplace one or two (emphasis on one or two) hardy andinexpensive fish in your aquarium. The fish waste contains theammonia on which the bacteria live. Don't overfeed them! More foodmeans more ammonia! Some suggested species include: common goldfish(for cold water tanks), zebra danios and barbs for warmer tanks, anddamselfishes in marine systems. Note: Do not use ``toughies'' or otherfeeder fishes. Although cheap, they are extremely unhealthy and usingthem may introduce unwanted diseases to your tank.Of course, there are many variations on the above that work. However,it is a bit difficult to give an exact recipe that is guaranteed towork. It is advisable to take a conservative approach and not addfish too quickly. In addition, testing the water to be sure nitratesare being produced eliminates the guesswork of determining when yourtank has cycled.Your tank is fully cycled once nitrates are being produced (andammonia and nitrite levels are zero). To determine when the cycle hascompleted, buy appropriate test kits (see the section)and measure the levelsyourself, or bring water samples to your fish store and let themperform the test for you (perhaps for a small fee). The cycling processnormally takes anywhere from 2-6 weeks. At temperatures below 70F, ittakes even longer to cycle a tank. In comparison to other types ofbacteria, nitrifying bacteria grow slowly. Under optimal conditions,it takes fully 15 hours for a colony to double in size!Your tank is fully cycled once nitrates are being produced (andammonia and nitrite levels are zero). To determine when the cycle hascompleted, buy appropriate test kits (see ) and measure the levelsyourself, or bring water samples to your fish store and let themperform the test for you (perhaps for a small fee). This processnormally takes anywhere from 2-6 weeks. At temperatures below 70F, ittakes even longer to cycle a tank. In comparison to other types ofbacteria, Nitrifying bacteria grow slowly. Under optimal conditions,it takes fully 15 hours for a colony to double in size!The desired species of nitrifying bacteria are present everywhere(e.g., in the air). Therefore, once you have an ammonia source in yourtank, it's only a matter of time before the desired bacteria establisha colony in your filter bed. The most common way to do this is toplace one or two (emphasis on one or two) hardy andinexpensive fish in your aquarium. The fish waste contains theammonia on which the bacteria live. Don't overfeed them! More foodmeans more ammonia! Some suggested species include: common goldfish(for cold water tanks), zebra danios and barbs for warmer tanks, anddamselfishes in marine systems. Note: Do not use "toughies" or otherfeeder fishes. Although cheap, they are extremely unhealthy and usingthem may introduce unwanted diseases to your tank.
Soon, bacteria called nitrosomonas will develop and they will oxidize the ammonia in the tank, essentially eliminating it. The byproduct of ammonia oxidation is . So we no longer have ammonia in the tank, but we now have another toxin to deal with - Nitrites. Nitrites are just as toxic to tropical fish as ammonia. If you have a test kit, you should be able to see the nitrite levels rise around the end of the first or second week.