There is almost no occurence of nitrite in a tank with fish where one should do a water change as a solution. There are two reasons why this is the case.
The first is how nitrite affects fish. it enter through the gills, gets into the blood.
Nitrite
Nitrite enters the bloodstream through the gills and turns the blood to a chocolate-brown color. Hemoglobin, which transports oxygen in the blood, combines with nitrite to form methemoglobin, which is incapable of oxygen transport. Brown blood cannot carry sufficient amounts of oxygen, and affected fish can suffocate despite adequate oxygen concentration in the water. This accounts for the gasping behavior often observed in fish with brown blood disease, even when oxygen levels are relatively high............
Luckily, although we often cannot prevent the occurrence of high nitrite, its effects can be minimized or neutralized safely and economically. Sodium chloride (common salt, NaCl) is used to “treat” brown blood disease. Calcium chloride can also be used but is typically more expensive. The chloride portion of salt competes with nitrite for absorption through the gills.
Maintaining at least a 10 to 1 ratio of chloride to nitrite in a pond effectively prevents nitrite from entering catfish. Where catfish (or
other fish) have bacterial and/or parasite diseases, their sensitivity to nitrite may be greater, and a higher chloride-to-nitrite ratio
may be needed to afford added protection from nitrite invasion into the bloodstream.
If you go to the article in the cycling section and read the section on Nitrite, it gives step by step insrtuctions for how to deal with nitrite without needing a water change.
The second reason we do not want to do a water change is how the bacteria actually function. The nitrite bacteria are triggered to reproduce when nitrite levels are greater than the existing bacteria can use. In this case, the bacteria begin to reproduce at a faster rate than they are naturally dying and reproducing at and this results in more of them being created/
When we change water to lower the nitrite reading we will not cause the reproduction we need. This in turn means the will be nitrite issues for longer and the fish are not being protected. By addint the chlporide in salt we protect the fish from the nitrite while allowing for the bacteria to reproduce as rapidly as they can to handle the nitrite. Bear in mind it takes 24 or more hours for the nitrite to leave the fish. But this assumea that there is not any nitrite still in the water. So,while a water change may lower the level of nitrie, it will still be entering the fish and staying there for a while. Only chloride protects the fish otherwise you have to wait while it continues to let more harm be done before you have sufficient bacteria to end the situation.
We cannot do something similar for ammonia or nitrate We have no option other than a water change in terms of lowering ammonia levels. Yes, this means the true solution of having more bacteria created from reproduction will take longer, but it is what we have to do to protect the fish since we cannot prevent the harm from ammonia or nitrate the way we can block the nitrite from doing so.
As the rescue article clearly states, the amount of salt required to block the nitrite is pretty low. There are almost no fish which will not have way more benefit from the salt than any harm you think it might produce. I recently worked with a member having nitrite issues at .25 ppm. this was in a 75 gal. tanl. The amount of salt needed to block that level of nitrite was 1/8 of a teaspoon. We used 64 gallons as the actually water volume to account for substrate, decor and the fact we do not fill tanks to the top.
This was a tank with fish in it. None of them dies, none of them were gasping at the surface. When the nitrie levels spiked hiher all that was needed was to add more salt at the rate of 1/8 teaspoon for every .25 ppm the nitrite increased.
Consider that water changes tend to stress fish and that stress weakens their ability to fight of diseases etc. So, having to do lots of water changes to [protect fish has it's potential downside. So what do think makes the most sense, to reduce the level of nitrite but not to stop more from entering your fish and spend all the time and effort big water changes require. Or instead, you just addia small amount of salt to your tank and prevent the nitrite from even entering the fish. (
Hint- add the salt.)
