Nitrite tests always inconsistent

[Jess]

Most of the time when I test my nitrites, the first one looks like the bottom tube and the second time looks like the top tube. These tests were done literally one right after the other. 

I fill a beaker with aquarium water, then use a 3ml plastic dropper to fill my API test tubes. Then I shake the indicator solution, dispense 5 drops, cap and invert the tube for 5-10 seconds. Then I do it a second time.  I rinse the tubes, shake them out, and let them dry until the next day. Test kit is not expired; I bought it brand new in August and just opened it in December. 
 

Why is it like this?  It does this almost every time I test.  I sometimes test 3 times. The latter two tests show up light blue, no trace of purple. So what’s going on?  The only other test that gives me problems is the API nitrate test; it consistently reads higher than my Salifert nitrate test. If it’s relevant, the pH is 6.0 lately. I’m not sure why...I don’t have any fish in it and I do 10-50% water changes every few days. Just plants and snails. I have ADA Tropica and it was dropping my pH to 6.2-6.4 but lately more like 6.0. I am not sure which test to believe. The tank has been running for almost 2 months. Ammonia always tests 0 (since just over 3 weeks ago I guess). 

I’m just wondering what could be causing this...never had it happen that I can remember  

Thanks for your help! 

Edited January 21, 2021 by Jess
Trying to add picture from my phone

[Jess]

Sorry - there is some bug in the forum. When I added the picture from my phone, it was saved but didn't show in the post.  After entering edit mode from my computer and saving (no changes made), now it shows up. Hope someone can offer suggestions about this!  I'm going to buy the Salifert nitrite test kit to see if I can shed some light on the problem. There test kits are much easier to use anyway.

[gardenman]

Most of the test kits have a time window in which to read the tests. My API tests for Nitrite say to wait five minutes for the color to develop. I suspect the longer you wait the more color develops. If you're doing one then the other one the first one will have more time for the color to develop than the later one, so you'd see different results. They key with most test kits is to read them at the time specified and assume (hope) that's the right number.

[Jess]

21 minutes ago, gardenman said:

Most of the test kits have a time window in which to read the tests.

I thought this, too!  I have left them for up to 6 hours.  For the first half-hour, I checked every 5 minutes.  Then I checked every half hour.  At the end of 6 hours, they both looked exactly like this.  I've repeated that 3 times.   

The color develops to this point within 5-6 minutes (you're right...I run the tests about 30 seconds apart instead of having another person run it at exactly the same time.  I'll try that today though.)  Then these colors stay like this for up to 8 hours (the longest I've left the tubes without rinsing).

Edited January 21, 2021 by Jess
Clarification and additional info

[Tanked]

For your pictures: try logging off this site and your browser, then start fresh.  

For the tests:  It sounds like there is a problem with your testing procedures.  The link below is the official API  nitrate test video.  Additionally, I would wash your vials in the water you are testing before the test, and sacrifice one drop of each solution to a paper towel before placing the correct number of drops in the vial. This will help insure even drops.   As @Gardenman, said, there is a test window.  Test results may degrade over time.

If you don't have any fish, I am curious as to why you are doing "10-50% water changes every few days"? If you are for looking for perfect numbers.  stop.

I hope this helps.

 

 

[Jess]

Thanks for the link.  I'm actually testing nitrites, not nitrates (see picture - not a nitrate test), but I did look up the corresponding video just to be sure I'm following the correct procedures.  I can see how you jumped to that conclusion though; most people don't follow the directions for the nitrate test and end up always reading 0ppm nitrates.  Actually, my problem with the API nitrate kit (why I use Salifert instead) is the resolution.  To my eyes, 10ppm and 20 ppm colors look similar, which means I have little confidence from 6ppm all the way to close to 80ppm (eh...realistically let's say more like 50ppm...).  For a planted tank, I am more comfortable with a little more resolution.  As for why I change 10% every few days (50% is fairly rare...I'm settling into 10-30% being most stable):  there are a few reasons, but mainly my snails poop like crazy and my plants do not uptake enough nitrogen to keep my nitrates at a level I'm comfortable with for keeping algae under control (they poop like crazy because I'm still adding plants and some are still converting - lots of dead and dying plant matter for them to eat).  When my nitrates climb above 50ppm, I do a small water change.  I prefer this over massive water changes once every week or two.  I'm not chasing "perfect" levels, I'm after stability while my tank is still settling in.

Back to the nitrite tests: I just ran two tests side-by-side, rinsed both with filtered water, etc.  They both came up the same this time - 0ppm.  The only difference is that I rinsed twice with filtered water (most of the time I'm lazy and rinse once with tap water). The other difference is that these were rinsed actually 4 times: twice after I used them yesterday and twice more today before the test.  So I assume this is related to some residue inside the test vial even after I do my normal (i.e. not OCD-level) rinsing.

My conclusion is still to buy the Salifert kit.  I have Salifert kits and I like them better - plastic vials with a wider base, so they are not breakable and easy to clean.  This should solve my "user error" problem.  They are more expensive, but it's clear to me those features make it easier for me to get accurate results so it's worth it.

I consider this case "closed" and thank you all for your help!

 

 

[L.W. Wetarm]

20 minutes ago, Jess said:

My conclusion is still to buy the Salifert kit.  I have Salifert kits and I like them better - plastic vials with a wider base, so they are not breakable and easy to clean.  This should solve my "user error" problem.  They are more expensive, but it's clear to me those features make it easier for me to get accurate results so it's worth it.

The Salifert nitrate test is my go to. Much easier to follow directions accurately....easier to read results.