Timing of Test Strip Readings

[kjfhg]

I have noticed that the longer I wait to read my Co-op test strips the nitrate color changes. It will show one color at 1 minute and 2-5 minutes will have a darker nitrate color. The bottle says to read at 60 seconds but I'm nervous about the higher nitrate reading after a longer period of time.

Advice and/or thoughts?

[Blaha]

The water will also begin to dry but the nitrates don't evaporate the same rate, so the drop on the strip will get smaller but the nitrates will stay around the same. That'll give a higher concentration by volume.
The strips also work by chemical reaction which needs some time to happen but if you wait too long it's reacted too long, like over cooking food in an oven.
A mix of those two factors would make it seem higher after a longer period of time.

I find it useful to use my phone timer, dip the multi-purpose strip and start the timer. Then stick the ammonia strip at 30 seconds. Then after 30 seconds you pull out and check the ammonia then check the multi-purpose right after. The timings right for both strips and you get to check all the parameters at once.

[Streetwise]

I am no expert on testing, but I have learned to be careful about how I place my test strips so that the pads don’t leach fluid to each other.

[Odd Duck]

On 10/11/2021 at 2:14 PM, kjfhg said:

I have noticed that the longer I wait to read my Co-op test strips the nitrate color changes. It will show one color at 1 minute and 2-5 minutes will have a darker nitrate color. The bottle says to read at 60 seconds but I'm nervous about the higher nitrate reading after a longer period of time.

Advice and/or thoughts?

Timing is everything when you’re reading test strips like that.  Trust the 60 second reading.  Also after dipping, make sure to tap off the extra water and lay the test strip down on something absorbent so the colors don’t spread between the blocks.  If the color spreads that means the reagents have spread and it can invalidate the results.