How long after dipping our test strips still accurate?

[Corbidorbidoodle]

So, you know how on test strips, a couple of the squares you read right away, and a couple of them you read after 30 seconds...

But how long after they come out of the water are they still accurate? Like, a minute or two?

I'm thinking specifically of the nitrates square. At 30 seconds they don't show any nitrates. But after about a minute they show about 40 ppm.

[Biotope Biologist]

It depends on the test strip but usually once they dry out they are no longer accurate as the reagent in the test strip reacts with the air.

 

Id say for me personally I can leave them out for about two minutes before the colors start changing due to drying out.

[jwcarlson]

What do the instructions that came with the strip say?

I don't really look at anything except nitrites and nitrates on the Co-Op test strips.  And I don't care about what the chart says for PPM.  If I dip it in for the three seconds and five seconds after I pull it out, the nitrate square is getting pretty pink, I know there's a lot of them.  On my discus tank there's barely any color on it after a minute, but if I don't pitch it right away the nitrite and nitrate squares show a tiny bit of color after it dries over 10-30 minutes (or a day). 

Whatever process that's designed around that reaction, there's a reason they give you a time after which to look at it.  Go by the instructions on the container and (in my opinion) don't use it to try to quantify how much nitrate or nitrite you have, but simply use it was a rough estimate.  If I dip in my planted tank and there's a very light pink after one minute, I'm going to give them some Easy Green.  If I dip and it's a deeper pink, but not boldly pink.  I wait on the Easy Green.  If it's dark pink I need to do a water change.

If for some reason I need to know "exactly" how many PPM of something I have... that's what the master test kit is for.

Edited March 9, 2022 by jwcarlson

[Corbidorbidoodle]

Yeah, I just use them to see if anything is WAY out of wack. I'll either do the liquid test or take it to the LFS for more specifics. But I was just kinda wondering of you have to check it at exactly 30sec or if there's a window.

 

[jwcarlson]

On 3/9/2022 at 3:58 PM, Corbidorbidoodle said:

Yeah, I just use them to see if anything is WAY out of wack. I'll either do the liquid test or take it to the LFS for more specifics. But I was just kinda wondering of you have to check it at exactly 30sec or if there's a window.

 

I'd look after 30 seconds and then look every minute after for say, 10 minutes, and see if there seems to be a time at which the colors get extra screwy.

[Corbidorbidoodle]

Oh, sure. Cuz it'll probably accelerate at some point.

[Bev C]

I use ACO strips   the most i stopped using APi liquid always stayed blood red  even shaking the bottle like crazy .. i have another  liquid test  to double check  because i have nitrates and phosphates in  tap water but have best luck with ACO strips  i leave them in tank about 5 seconds swirl it around set timer a minute like the directions  says and then i look …   i say  the first minute is the best to read after the 1 minute time mark 

Edited March 10, 2022 by Bev C

[StanF]

I also  use the aquarium coop test strips.  The instructions say to swirl the strip in the tank water for 3 seconds and to compare the results 60 sec after taking it out of the water.  You have to wait the full 60 secs for the color to develop.  If you wait too long, the color continues to darken and will give a false reading.  I set a one minute timer on my phone so I don't forget.

StanF

[Tanked]

I previously used Tetra strips.  When I asked, Tetra also responded that their test strips had to be read at 1 minute for best accuracy.  I doubt that there is a huge difference in test strips.  As @StanFsaid If you wait too long, the color continues to darken and will give a false reading.

[CT_]

IME it is accurate at exactly-ish 1min for nitrate nitrite.  any longer nad it reads too high. 

gh kh seem to be readable really fast and don't change unless the water from the pads mixes by accident.

 

I don't pay attention to the chlorine because its always 0.  ph doesn't work for my batch (but it seems to be specific to my tube of them) but I assume that one is pretty immediate too.

[Corbidorbidoodle]

Thanks for the tips. I got the ACO strips and I really like them. Interesting about the Chlorine pad, cuz mine tests "0" right out of the tap.

[Apulo]

Just to add my two cents, I tested ammonia with an ACO strip and after swooshing it around for 30 seconds it was clean.

I let it sit unintentionally for a few minutes and it turned dark green so in a panic I tested with my API Master Kit which read zero.

So yeah, letting them sit too long might give a false reading.

[Odd Duck]

Any test strips like this can get a false reading if read too long after wetting.  Very important to read in the time frame recommended and to dip for the time frame recommended.  You also don’t want them to sit in a puddle of water since reagents can cross react between pads.

You should dip, gently tap off extra water sideways (not lengthwise), then hold fairly level, or lay down flat on a paper towel would be best, so any water isn’t running between pads, and read at the indicated time, not before and not after, or you will NOT have accurate results.

No matter how good the quality control is, there will be times when the strips may show inaccurate results.  Double checking with another testing system like the drop kit is always a good choice if there is any doubt about your results.

Edited April 1, 2022 by Odd Duck