Nitrate and ????

[TwoTankAmin]

There is actualy science on how deep beds work. For fish keeping one way to go is to have live plants in the substrate, This may not always be possible, but here si what should happen when you have say 3 inches of smaller sized gravel and you plant it.

Nitrification and denitrification in the rhizosphere of the aquatic macrophyte Lobelia dortmanna L.
Nils Risgaard- Petersen, Kim Jensen
https://doi.org/10.4319/lo.1997.42.3.0529
First published: 01 May 1997

Abstract

Nitrogen and O2 transformations were studied in sediments covered by Lobelia dortmanna L.; a combination of 15N isotope pairing and microsensor (O2, NO3−, and NH4+) techniques were used. Transformation rates and microprofiles were compared with data obtained in bare sediments. The two types of sediment were incubated in doublecompartment chambers connected to a continuous flow-through system.

The presence of L. dortmanna profoundly influenced both the nitrification-denitrification activity and porewater profiles of O2, NO3−, and NH4+ within the sediment. The rate of coupled nitrification-denitrification was greater than sixfold higher in L. dortmnanna-vegetated sediment than in bare sediment throughout the light–dark cycle. Illumination of the Lobelia sediment reduced denitrification activity by ∼30%. In contrast, this process was unaffected by light–dark shifts in the bare sediment. Oxygen microprofiles showed that O2 was released from the L. dortmanna roots to the surrounding sediment both during illumination and in darkness. This release of O2 expanded the oxic sediment volume and stimulated nitrification, shown by the high concentrations of NO3− (∼30 µM) that accumulated within the rhizosphere. Both 15N2 isotope and microsensor data showed that the root-associated nitrification site was surrounded by two sites of denitrification above and below, and this led to a more efficient coupling between nitrification and denitrification in the Lobelia sediment than in the bare sediment.

Full study here https://aslopubs.onlinelibrary.wiley.com/doi/epdf/10.4319/lo.1997.42.3.0529

If you go to the paper you will find links to more papers on this topic as well as to other papers which cited this study.

Lobelia is not the only plant that does this.

I almost never test for nitrate. I do 50-60% weekly water changes on all my tanks without testing. As I have said before, I do not know of any fish dying because their water was "too clean." (Note, this is not the same thing as being too pure.)