Thoughts on Nitrate Levels and Water Changes

Uberhoust

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Just some thoughts:

  1. If you have a limited amount of water you can use for water changes less frequent larger changes remove more contaminants than smaller more frequent changes of the same resulting amount. Why? Primarily you are removing more water at a high concentration and replacing it with a larger amount of clean water, after each change, overall the average concentration that the inhabitants are exposed to is lower overall than with smaller changes. Example: Assuming a weekly increase of 2.5ppm in an aquarium a 50% change per 4 weeks results in a maximum of 20ppm but with an average of approximately 15ppm. Whereas for the same rate a 12.5% change weekly results in the same maximum but an average of approximately 18 ppm over the entire time frame, but the variance the the concentration is less.
  2. Rate of NO3 concentration increase over a time period, along with the frequency of water changes, and the percent changed determine the maximum Nitrate in the aquarium overtime. Starting from a low concentration or high concentration will limit to the same point.
  3. The rate of NO3 concentration change could be used as a rough indicator of the bioloading within the aquarium. The largest issue with this is that the accuracy of the Nitrate tests are too coarse for truly meaningful calculation of rates, but we can estimate.

I have attached an excel spreadsheet that allows you to enter that nitrate value just after a water change, and the nitrate value just before a water change. With that information and the number of hours between the reading it will estimate the rate of Nitrate production in that tank. Using that information it will give you an estimation of the idea percentage to change to maintain a maximum nitrate value.

Example 1 (NO3 2.5 ppm per week 50% water changes every 4 weeks, starting value 70 ppm)
1621377844154.png


Example 1 (NO3 2.5 ppm per week 12.5% water changes every 1 weeks, starting value 70 ppm)
1621378006703.png


Example 3 (2.5 ppm of NO3 per week, targeting max of 30 ppm, biweekly water changes)
In this example the maximum concentration is still approaching 30ppm after a year, it will never get there but will be close.
1621378515040.png


Overall frequent larger water changes are difficult to improve on but if you have limited water resources, ie you have to "make" your water it might be beneficial to do less frequent changes. Frequent water changes are often opportunities to clean the glass, clean the filters, and trim and look over the plants, and their benefit is not captured with this spreadsheet.

Feel free to experiment with the spreadsheet. The entry fields are in peach, but the sheet is not locked or otherwise protected. Let me know if you find any errors. I used a iterative approach rather than a limit approach, primarily because it was a simpler approach.
 

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  • Nitrates.zip
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Sunnyspots

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I thought fewer, larger changes would be better, but then found that my very soft water would benefit from frequent smaller changes to minimise shifts in pH. So I guess for some people that would need to be taken into account rather than focusing on nitrates. I know that isn't the point of your piece (and masses of work!) but thought I might add it as another thought. I hope you don't mind :)
 
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Uberhoust

Uberhoust

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The spreadsheet only looks at one aspect, nitrate. The there are other factors involved. In my case I have found that 40% weekly is a reasonable balance between maintaining the water chemistry and reducing the overall maintenance. Even amongst my tanks some do better with different schedules.
 

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