Trate

[Jimmy74]

I know 0 is best. That aside, I’m reading below 20, below 40, ppm nitrate is good for most freshwater. So which is it? I know there’s exceptions. I’m talkin broad. So is 40 any worse than 20?

 

[itiwhetu]

Below 20, 40 is to high.

 

[Essjay]

Ideas on how much nitrate is safe has changed over the years which is why you'll find different sources saying different things. When I first started keeping fish it was widely advised that nitrate was OK up to 100 ppm. Then it was 40, and later 20 ppm.

The fish we keep come from water with no nitrate. The closer our nitrate is to zero the better.

 

[PheonixKingZ]

Between 5-20ppm is usually best. If you are reading 0 nitrate, usually your test kit is messed up or you did the test wrong.

It’s perfectly OK to have 0ppm nitrate, as long as you drive it that low naturally. (By the use of organic carbon) When done unnaturally (by the use of chemicals) it can negatively impact the tank in many ways.

 

[Essjay]

My tank nitrate is virtually zero, but I'm lucky because my tap nitrate is below 5 ppm (my water quality report says 4 ppm). As I have a lot of floating plants, no nitrate is made in my tanks.

 

[Byron]

I concur with keeping it below 20ppm, and as low as possible. As others especially @Essjay mentioned, our understanding of the detrimental effects of nitrate have changed over the decades. There are very few studies using ornamental fish (our tropical aquarium species), and most of the few studies there are were focused more on food fish or sport fish being raised in ponds for release into rivers/lakes.

Within the past decade or so the biologists in this hobby have begun to better understand the impacts of nitrate. There are species much more sensitive to nitrate, species like mollies and all cichlid; high nitrate has been associated with diseases such as bloat, shimmies, hexamita and hole in the head in cichlids. All of our fish species have evolved to function in water with basically no nitrate, so physiologically we should expect problems if we expose them to nitrates. Another understanding is that unlike ammonia and nitrite, whose effects are more rapid and serious, the effects of nitrate are slower to appear, depending upon the level, the species, and the time of exposure.

The effects of nitrate are also not fully understood, but Neale Monks says it is probably best to think of it as a gradual weakening of the fish. At some point, the fish will likely succumb to some disease, or just die, as a result of the weakening effects of nitrate.