Nitrite Phase of Cycling

[Sa777]

My 20 gallon tank has been cycling for about three and a half weeks now. I'm doing a fish cycle with 1 rainbowfish, 1 red-tailed shark, and 2 peppered corys. All fish seem to be completely healthy and happy. I had not tested my water for about three days and then, about four days ago I did. Ammonia was gone, and Nitrites were about as high as my test read. There were also some Nitrates present. All of this happened over the course of the three days I didn't test. I've been doing daily 20% water changes since and the nitrites have not dropped, they are still at about 3-4 ppm. Have my nitrites spiked? I have nitrates, so is it almost over? Give me your best estimate as to how much time I have remaining.
P.S. I put in some bacteria when I first started and I have no live plants in the tank.

 

[Mebbid]

I would say probably 2 weeks before you're done. The nitrite phase takes close to twice as long as the ammonia phase does.

That being said, it would be best to do a couple 50% water changes to get those nitrites down. They aren't good for fish.

 

[Linwood]

The more common nitrate test (API liquid) is not accurate when there are nitrites present, so I wouldn't bother even testing until the nitrites are gone.

 

[Mebbid]

The more common nitrate test (API liquid) is not accurate when there are nitrites present, so I wouldn't bother even testing until the nitrites are gone.

Uhhh... what?

 

[ScotJudd]

I've never heard that before, Linwood, are you sure of that? Where have you read that?


Sent from my iPhone using Aquarium Advice

 

[Linwood]

I've never heard that before, Linwood, are you sure of that? Where have you read that?

Sure? It's hard to be sure of anything on the internet, but my nitrates dropped significantly at the end of my cycle without a water change, and I went looking for info.

What I found was repeated in numerous places, but I don't have a way to verify. For example here:

Beginner FAQ: Test Kits

Look at the third paragraph under nitrate test. I found that repeated in numerous forum postings, though of course they could all have originated in one place.

What I haven't been able to find is a discussion of the actual chemistry of the nitrate test kind in API, which might allow one to verify if true.

But since I saw the nitrate reading go down, I was willing to believe it. However, that said, I didn't try to quantify whether the conversion rate (from bacteria) and the conversion rate (for the test kit) would be comparable, and how it should impact the reading.

I've also read very frequently that the API Nitrite test is inaccurate at high readings, or more precisely it reads quickly (deep purple) and if left to sit for the recommended 4 minutes, it turns back to a blue that would indicate light nitrites. So most places I've seen recommend to watch it -- and if it goes deep purple quickly you are basically off the chart high and don't keep looking.

I don't actually know this for a fact, but rather one of those "seemingly repeated enough to make it true" internet facts, so use it accordingly.

Any chemists around who can state more authoritatively how it works?

PS. All that said -- in a cycle there's really very little point in checking nitrates until your nitrites are gone -- you need to be changing water to keep nitrites reasonably if there's stock in there anyway (and that will flush out nitrates also), and you aren't "done" until the nitrites are zero, regardless how many nitrates you are getting.

 

[Mebbid]

I did some digging while I was sitting around for a minute and you're correct. There are 2 main ways of testing nitrates. The first is to use the dip stick which uses a material that reacts with the nitrate directly. The second is the liquid test kits like the API kit which changes the nitrates into nitrites and then gives a reading based off of that.

However, looking at the API nitrate test card the readings go 0 - 5 - 10 - 20 - 40 - 80 - 160 whereas the nitrite card maxes out at 5ppm.

With such a high range test kit, if your nitrites are high enough to mess with the nitrate reading you have much much bigger problems than an inaccurate nitrate count.

 

[Linwood]

With such a high range test kit, if your nitrites are high enough to mess with the nitrate reading you have much much bigger problems than an inaccurate nitrate count.

Is the way the chemical conversion and measure works, the process 1 for 1?

I.e. if you (really) have 5ppm nitrates and 5ppm nitrites, does the nitrate test show 10ppm?

The 5ppm nitrite will turn, naturally, into something like 7ppm, though conversion by the nitrifying bacteria, but that difference is insignificant. What I'm asking is does the chemistry of the test kit conversion do it (nearly) 1:1 as well?

 

[DeeLee2013]

Amazingly informative. Definitely following!


? Diana Lee ?
? the St. Augustine Redhead ?

 

[Mebbid]

Is the way the chemical conversion and measure works, the process 1 for 1?

I.e. if you (really) have 5ppm nitrates and 5ppm nitrites, does the nitrate test show 10ppm?

The 5ppm nitrite will turn, naturally, into something like 7ppm, though conversion by the nitrifying bacteria, but that difference is insignificant. What I'm asking is does the chemistry of the test kit conversion do it (nearly) 1:1 as well?

Going by molecular weight 1ppm of nitrite is approximately 1.33ppm of nitrate. If the test kit truly turns nitrate into nitrite then that should be the correct conversion.