Nitrates tested high day after a water change but fine days later

[Jicklenop]

So as the title says I did about a 20% (5 gallons) water change last Sunday and tested nitrates on Monday. They came out around 13.9ppm which was very surprising because that was slightly higher than they were before the water change. I left it at that for a few days and tested again and came out to 8ppm which made more sense to me. I feel like I've read high nitrates like that before the day after a water change before but since it was around 10, I was just planning on a 10 gallon change the next week instead.

Does anyone know why the nitrates may have tested high? I use the hanna Nitrate hr checker. I can't tell if it's an improper reading or what exactly is going with the readings.

 

[Dan_P]

So as the title says I did about a 20% (5 gallons) water change last Sunday and tested nitrates on Monday. They came out around 13.9ppm which was very surprising because that was slightly higher than they were before the water change. I left it at that for a few days and tested again and came out to 8ppm which made more sense to me. I feel like I've read high nitrates like that before the day after a water change before but since it was around 10, I was just planning on a 10 gallon change the next week instead.

Does anyone know why the nitrates may have tested high? I use the hanna Nitrate hr checker. I can't tell if it's an improper reading or what exactly is going with the readings.

I assume that you are using the high range version. There might be a quality issue with the reagent. For me, when the reagent does not flow readily out of the packet, the reading will be low. This means low readings are the bad ones, higher ones more correct (I checked this with the low range Hanna nitrate Checker).

 

[folsomreefing]

Can only speculate but if you stirred up a bunch of stuff in the process of the change nitrifying bacteria could have consumed it causing a nitrate spike which was then consumed by something in your tank (corals, algae (micro or macro), etc)

 

[Randy Holmes-Farley]

Or nitrite stirred up.

In any case, the effect is quite small and not worth worrying about, IMO.

 

[deome]

What kind of water are you using for water changes? Tap water can introduce nitrates if it's not properly RODI-fied. Also could be stuff stirred up by the water change. Could also be a testing error, sometimes I don't get the entire testing packet into the sample vial.

If it's going back to normal after a few days I wouldn't worry about it, bacteria are doing their job and can respond quickly to nutrient spikes.

 

[Jicklenop]

I wondered if it might be something about cleaning my sand bed, it had a rather large dusting of diatoms when I vacuumed some parts.

I think it's testing high because generally my tests are between 5 and 10 with only a few outliers like this.

I go to my LFS for saltwater, think they use reef crystals. Can't say I've tested directly from them to see how it is.

Thanks you all for the input

 

[Righteous]

I have a Trident NP testing daily and I consistently see a jump on nitrate the day after cleaning the sandbed, which drops again in the following days.

 

[Jicklenop]

I always felt like the day after was safe enough to let it all settle. I might have to offset my testing a little more to avoid it.

 

[Reefahholic]

That’s likely due to the instability of the water change, and the slowed or stalled consumption.