As mentioned, average filtration does not remove nitrate, because nitrate is waste product of filtration.Filtration?
Frequent Water changes are the best way to reduce nitrate.
An occasional large water change will not make much of a dent.
I do 30 to 40% every other day water changes on my 300+ gallon system, and nitrate remains undetectable.
My latest nitrate test above.
But I also use lots plants (aquatic and terrestrial) , because they directly use nitrate.
But to make a dent, the plant weight must outweigh the fish many times over.
In the U.S. the MCL (maximum contaminant level) for for nitrate in drinking water is 10ppm, most systems don't come close to that.
Where I worked as a chemist at the water purification plant, average nitrate in tap water was 0.20 ppm.
High nitrate is usually only problematic in drinking water, in agricultural areas where high amounts of fertilizer are used
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