Has anyone gotten "false positive" test results?

[patsfan1130]

I ask because I just did my water tests and got some unexpected results. They are as follows...

PH- 8.22
SG- 1.025
Temp- 78.4
CA- 430
KH- 12
PO4- undetectable
NH3- undetectable
NO2 0.2 ???
NO3- 2.5

I usually dont test for NO2 as the tank is established but figured I would this morning. I use Salifert test kits (brand new). The NO2 reading seems very odd to me and I am thinking that the test is reading a false positive. I am going to buy another test kit to see what type of result it yields.

Here is my setup

90 AGA
4'' LS substrate
120lbs LR
MR-1 skimmer
aquaclear 500 (I clean this daily)

I do 10% water change weekly. dose B-ionic daily. feed every other day (small amounts). The last thing I added to the tank was a RBTA about a month ago. All inhabitants seem to be very happy and are displaying no concernig behavior. They are...

Hippo Tang
Maroon clown
Flame angel
Coral beauty

Frogspawn
Torch coral
Plate coral
some xenia,mushroom & various polyps
about 100 assorted snails (turbo,cerith,nassarius)

I'm not overly concerned but was wondering if anyone ever had something like this happen before.

Mark

[Ninong]

I use Salifert's nitrite test kit. I try to be extremely accurate in measurement of the 1 ml of tankwater and the one level spoon of the NO2 powder and then I am careful to exactly time the test by swirling the test tube gently for exactly 20 seconds and then allowing it to rest for exactly 3 minutes before quickly taking my reading. Allowing it to rest longer than 3 minutes allows the color to darken and you will get a higher result.

However, even with all of those precautions and even with sometimes performing the test twice in a row because I didn't like the initial results, I always get a positive reading when holding the test tube firmly against the white part of the color chart and looking through the side of the tube. I have never observed any color at all looking down into the tube but when I hold the tube against the white chart and look through the side I usually get a match for either the 0.5 square or the 1 square, meaning I am getting a reading of 0.05 ppm or 0.1 ppm. I don't believe I have ever gotten a match for the 2 square (0.2 ppm) such as you are getting. Maybe you allowed it to rest longer than 3 minutes before taking your reading?

I don't know what to think about this but it hasn't concerned me very much because when I get a nitrite reading of 0.05 it is usually in conjunction with a nitrate reading of less than 3 ppm and when my nitrite reads 0.1 ppm it usually matches up with a nitrate reading of around 5 ppm. Even when I happened to measure nitrate readings of approximately 1 ppm, I was still getting some slight pinkish coloration when looking through the side of the test tube in the nitrite test, which corresponds to about 0.05 ppm nitrite.

My skimmer was turned off for two weeks last month while I was on vacation in California and when I returned my tankwater tested at 10 ppm nitrate and 0.1 ppm nitrite. Right now I'm testing 5 ppm nitrate and 0.05 ppm nitrite. Maybe one of these days I'll get better and more expensive test kits for both nitrite and nitrate and see if they make a difference. I have Salifert's ammonia test kit, too, but it's only useful for testing catastrophic ammonia readings. It is not capable of testing below 0.5 ppm total ammonia.