Api No2- Liquid Test Inaccurate?

[Seed]

Didn't know where else to post this.

I just completed two fishless cycles. Towards the end, when the ammonia was processing within 12 hours, I noticed something weird. I was adding enough ammonia to both of these tanks to give me 5 PPM ammonia. This concentration I confirmed with both calculations and with the test kit (as best I could, the test kit is hard to read, but was colored in the range I predicted via calculations). This is the first time I've cycled fishlessly, so I was a bit obsessive about the testing, i.e. testing more often than need be.

What I saw was strange and happened several times. The ammonia would test positive because it hadn't processed yet, showing between 2-4 PPM (hard to read on the API kit). Meanwhile the Nitrite test was completely off the charts. Keep in mind that the tank was processing everything within 12 hours. The test goes up to 5 PPM for NO2-.... yet NO2- and NH3/NH4+ have the same molar amount of nitrogen. So where was the extra nitrogen coming from that would process into NO2-? This was observed after adding ammonia to a tank that showed no detectable levels of NH3 or NO2-.

I have three conclusions:

1. From somewhere, extra ammonia was entering the system. Not likely, as the tank was barren.

2. NO3- for some reason was being reduced to NO2- in the presence of the ammonia solution I was adding to the tank. I've no earthly idea why this would happen, but since I could only observe this when ammonia solution was present and added to the tank, I decided that this was a possibility.

3. The API NO2- test is inaccurate at concentrations above 1 PPM.

Any ideas? I'm thinking that the NO2- test is good for showing that you have nitrites present, but not good for estimating concentrations.

 

[Bignose]

Are you sure you weren't just at the time between the growth of the ammonia oxidizing bacteria (AOB) and the nitrite oxidizing bacteria (NOB)?

That is, the AOB were able to process everything fast because their numbers were high, but the NOB numbers were still low because they hadn't had enough time to grow yet, so there was a backlog between the two? That would result in a large concentration of nitrite.

The other possibility is that tests are sometimes just wrong or expire.

What were the levels of nitrates during these tests? That would answer a lot -- if the nitrates were low then that would confirm the hypothesis that the NOB hadn't had a chance to grow up yet.

 

[Seed]

Are you sure you weren't just at the time between the growth of the ammonia oxidizing bacteria (AOB) and the nitrite oxidizing bacteria (NOB)?

That is, the AOB were able to process everything fast because their numbers were high, but the NOB numbers were still low because they hadn't had enough time to grow yet, so there was a backlog between the two? That would result in a large concentration of nitrite.

The other possibility is that tests are sometimes just wrong or expire.

What were the levels of nitrates during these tests? That would answer a lot -- if the nitrates were low then that would confirm the hypothesis that the NOB hadn't had a chance to grow up yet.

Well... Here is my thinking. Even if the NOB hadn't developed as much as the AOB, the ammonia levels were dropping between 1-3 PPM. So, and this is assuming a buildup of NO2- without the NOB utilizing it immediately, wouldn't I see between 1-3 PPM NO2-? To clarify my thinking NO2- and NH3 = same amount of nitrogen in each compound, so I would expect that if say 1 mg/L of NH3 had been processed into NO2-, that the results of the tests would be 1 mg/L NO2- and 4 mg/L NH3 (assuming a starting point of 5 PPM NH3 for discussion's sake).

What I saw instead was around 1-3 PPM NH3 processed and the NO2- was off the charts, indicating a lot of nitrogen came from somewhere because the amount of NO2-, according to the test, was so much greater than the NH3 processed.

It is possible that the test is bad, but it's only two months old. No idea how long it sat on the shelf before I bought it though.

And I didn't check nitrate levels unfortunately. I know NO2- was being utilized though because the nitrites were processing within 12-15 hours down to undetectable levels. That's actually why I didn't bother with a nitrate test, because I knew that they had to be there.

 

[Bignose]

Except that in between times of feeding the AOB, the nitrite keeps building up because the NOB hasn't gotten to it yet. Feed the AOB 2 ppm one day, get 2 ppm of nitrite. Feed the AOB 2 more ppm the next day, get 2 more ppm of nitrite for a total of 4. And then 6 ppm, and so on... lots of nitrite will build up while the NOB colony grows. That's why you would test and get very high value of nitrite.

 

[rdd1952]

Along the same lines that Bignose is going, is the tank processing 4 ppm of ammonia back to 0 ammonia and 0 nitrite in the 24 hour period or since you said that you were near the end of the cycling proces, is there still some amount of nitrite left when you add ammonia back? If there is still nitrite present, then that would explain what is happening. As mentioned, you sould be adding 4 ppm of ammonia onto say 2 ppm of nitrite already present.

If they are both at 0, then I guess it is possible that some form of denitrification (which I definitely don't understand) is taking place where nitrate is being broken back down into nitrite. The part of this I've never understood is if there are anaerobic bacteria that denitrify nitrate into nitrite and then nitrite into something else, why would there ever be nitrate in the tank? Why would these bacteria not just process nitrite into what ever before he nitrobacters/nitrospiras process nitrite into nitrate? Sorry, off topic there.

The key question though is whther there is nitrite present in the tank though when more ammonia is added?

 

[Seed]

I saw this after both ammonia and nitrite levels had dropped to undetectable levels. Like I said, I tested a lot more than I probably needed to, but it went like this:

Checked the tank in the morning, NH3 & NO2- at undetectabler levels, I added the appropriate amount of ammonia to continue cycling the tank.

Checked a few hours later, depending on when I did this (checked over multiple days) the NH3 would drop between 1&3 PPM, but the nitrite test would be off the charts.

 

[rdd1952]

That is strange as my understanding is that it's pretty much a 1 to 1 change, i.e., 4 ppm of ammonia >> 4 ppm nitrite >> 4 ppm nitrate.