False positive nitrites, troubleshooting ideas

[EMeyer]

I've been dosing nitrates in several tanks lately (finally got nitrates back up to detectable levels). As a result, I've been doing nitrate tests again after I swore off NO3 tests long ago as useless.

With the seachem nitrate test, you test for nitrite in the process. So even if you arent looking for it you see results of NO2 while testing for NO3. Now obviously we dont expect to see NO2 in mature reef tanks and thats what I have typically seen. Until a couple days ago when I started seeing high NO2 levels in one of my tanks, while the other two remain undetectable as expected.

I dose all tanks the same, and all three had been showing ~1-2 ppm nitrate until this. Now obviously I cant trust the NO3 readings on my high NO2 tank, but the other two are remaining around 2 ppm nitrate and I've continued to dose all three the same.

I'm stumped -- this cant really be >10 ppm nitrites but I don't see where the false reading is coming from. I've checked
1. The source RODI used for topoff and WC, its clean
2. Its not interference from nitrates; the test reads zero nitrites using a 10 ppm NO3 standard
3. its not a dirty test well or a bad sample; I've run multiple tests in different test vessels including new clean test tubes

This has me stumped! The fish and corals seem perfectly happy. Any ideas what could be causing false high NO2 readings in only one of three tanks? Thanks for any ideas.

 

[EmdeReef]

What do you use to dose nitrates?

 

[EMeyer]

calcium nitrate. I have tested and the dosed solution itself reads zero on nitrite. Let alone the 1 ml per hour dose diluted in tank water.

 

[EmdeReef]

Unless your tank is going through a mini cycle I at least don’t know. FWIW 10ppm isn’t an issue.

#reefsquad?

 

[GoVols]

FWIW 10ppm isn’t an issue.

+1

 

[rkpetersen]

My first thought would be some issue with the test kit; I'd try a different nitrite test to see if it confirms.

My second thought would be that something has died and remained in the tank; ammonia-reducing bacteria being up to the sudden increase but nitrite-reducing bacteria reacting more slowly (as they typically do.)
Assuming you also have checked ammonia and it's flat zero.
If this is the case, your nitrite level should come back down on its own as the mini cycle ends.

 

[EMeyer]

The same test kit shows normal results with water from my other tanks, and a zero value on a standard solution of nitrate. I do not have any nitrite on hand to make a standard solution of that. On this basis while there may be something wrong with the test kit, I'm skeptical that it explains its odd behavior on this one tank.

 

[EMeyer]

Folllowing up and recording for posterity in case anyone sees something similar.

In the end, it looks like in fact I had a nitrite spike, not a false positive. Nitrites went back down on their own, and nothing appeared to suffer from it. Never observed a nitrate spike either but nitrate consumption rates are huge in these tanks, I am not surprised.

Just bizarre to see a nitrite spike ~1 year into the tank, without any known deaths or other major changes.

Biology is weird sometimes.