Dark Start: No Nitrate

[LL_Rowan]

Hello,
I'm currently 3 weeks into a dark start and everything was going as expected.
On the 21/01/25 the readings were:
NH3: 0.2
NO2: 8
NO3: 80

I did a 50% water change, and then went away for a few days.
I got home today and did another test, all the results were 0.

I was surprised there was no nitrate, so I repeated the test and got the same result. The tank doesn't have any plants or livestock, only aquasoil and rocks.
My only guess is that the nitrates are so high the test can't cope. (It's the NT Labs Test Kit).

What is going on?

 

[dw1305]

Hi all,

I got home today and did another test, all the results were 0.

I was surprised there was no nitrate, so I repeated the test and got the same result. The tank doesn't have any plants or livestock, only aquasoil and rocks.
My only guess is that the nitrates are so high the test can't cope. (It's the NT Labs Test Kit).

What is going on?

Try diluting your tank water with RO and see if you get a reading then?

Nitrate testing is much more problematic than most literature acknowledges.

Cheers Darrel

 

[LL_Rowan]

Hi all,

Try diluting your tank water with RO and see if you get a reading then?

Nitrate testing is much more problematic than most literature acknowledges.

Cheers Darrel

Thank you.

I've not got any RO but my tap water is pretty benign.

I've tried a 50:50 mix and a 1 to 5 mix (tank to tap), but still nothing.

Why is Nitrate testing problematic?

Cheers L

 

[dw1305]

Hi all,

I've tried a 50:50 mix and a 1 to 5 mix (tank to tap), but still nothing.

The only other mechanisms for <"nitrate loss is via anaerobic denitrification">, which is unlikely, so that makes the test kit prime suspect.

Why is Nitrate testing problematic

Just because all nitrate (NO3-) compounds are soluble, meaning that you have to reduce the NO3- to nitrite (NO2-) <"before you can produce a coloured compound that you can measure">. Because it is a two stage process that gives more chance for things to go wrong - <"No Nitrite, Nitrate.">.

Cheers Darrel

 

[LL_Rowan]

Thank you, I doubt it's anaerobic denitrification.

Thanks, interesting information about the Nitrate test.

If the tests are unreliable, what are the best ways of identifying nitrate levels?
I'll likely be adding plants this week, so I'm guessing monitoring their health will be an indication.

 

[dw1305]

Hi all,

If the tests are unreliable, what are the best ways of identifying nitrate levels?

You could get a <"nitrate ion selective electrode">, if you really want an empirical measurement.

I'll likely be adding plants this week, so I'm guessing monitoring their health will be an indication.

Yes. I'm not an unbiased observer, but I would recommend the Duckweed Index <"What is the “Duckweed Index” all about?">. It is based on <"The scientific background to the "Leaf Colour Chart""> and if that is good enough to feed <"half the World's population">? I'm going to say it works.

cheers Darrel