Diana Walstad (2014)
Ammonium and nitrite are detrimental to fish health. 1 Most hobbyists rely on filters (i.e., “biological filtration” or nitrification) to remove these toxins from the water. They do not consider using plants. Even hobbyists with planted tanks underestimate plants in terms of water purification. For they assume that plants mainly take up nitrates as their source of N (nitrogen).
However, the truth is quite different. Scientific studies have shown repeatedly that the vast majority of aquatic plants greatly prefer ammonium over nitrate. Moreover, they prefer taking it up via leaf uptake from the water, rather than root uptake from the substrate. Thus, plants can—if given the chance—play a major role in water purification. They are not just tank ornaments, aquascaping tools, or hiding places for fry.