Acceptable level of Nitrate


I've been wondering what level of nitrate people find acceptable in their aquariums.

Practical Fishkeeping says 40ppm is ok for tropical fish. Live Aquaria says 50ppm. I've always tried to keep mine as low as possible (10ppm or below)

This is from Algone: (Nitrate removal product)
Nitrates lower antibody production, affect the composition of the blood, cause kidney damage, decrease fertility, and also affect osmoregulation (ability to regulate fluids). A more indirect effect is fish stress. Nitrates, and the resulting decline in water quality cause stress on fish. Stress reduces the slime coat making the fish more vulnerable toward disease. High nitrates also contribute to lower dissolved oxygen levels in the water.
The Bottom-Line
Rising, or persistently high nitrate levels indicate and cause problems with water quality of the aquarium and consequently fish health. Nitrate levels should be kept at the lowest level possible and ideally should never exceed 10 ppm long term.

Here is a scientific paper: Nitrate toxicity to aquatic animals: a review with new data for freshwater invertebrates:
(Julio A Camargo, Alvaro Alonso, Annabella Salamanca)
Freshwater animals appear to be more sensitive to nitrate than marine animals. A nitrate concentration of 10 ppm can adversely affect, at least during long-term exposures, freshwater invertebrates , fishes , and amphibians. Safe levels below this nitrate concentration are recommended to protect sensitive freshwater animals from nitrate pollution. Furthermore, a maximum level of 2 ppm would be appropriate for protecting the most sensitive freshwater species.

And then there is this: António et. al. 2017 found no long-term effects from a level of 440 ppm. Monsees et. al. 2016 found the lower long-term damage level for adult cichlids to be 2,220 ppm. Science Direct, Semantics Scholar and James Cook University have several papers available all of which say a level of 440 ppm does no long-term damage to adult fish. A recent study exposed young salmon to 440 ppm nitrate for 8 months and they grew just as well as salmon kept at 1/10th that level.

If the scientists don't agree what are the chances that aquarium hobbyists will?? :~)

My opinion is that chronic low-to-moderate doses of poison can't be good for the fish even if they appear healthy. Just my opinion. On the other hand, a beer a day isn't going to make you sick, so maybe a little nitrate won't hurt either.

EDIT: FWIW, U.S. EPA has set 10ppm as the upper limit for human consumption in drinking water.Above that, it's not considered safe for children.


I like to keep mine no higher than 20ppm - if its orange on the api test, then im ok with that and so are my fish.

Of course this question also depends on the species of fish being kept - some are more forgiving in terms of nitrates than others.
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It was really interesting looking over the numbers of the studies, thank you for sharing them! I've looked through some other studies before and I came to the same conclusion as you did, that no one can really agree on the concentration of nitrates that would be considered dangerous. I also imagine the amount of nitrates a fish can handle will vary drastically depending on the species, and it could also depend on if the fish is wild caught or captive bred.

But we need to give people some numbers as guidelines, because just saying "We know nitrates are harmful to fish but we don't know exactly how harmful" isn't helpful at all. So even if the numbers end up being arbitrary, it gives people something to work off.

I like to use what I call the 20/40/80 rule, because it's easy for people to remember. It breaks down like this.

0-20ppm Ideal range, the goal number will vary depending on personal preference and tank setup.

40ppm The upper limit of safe. Time to do a water change to get the number down.

>80ppm Not a good place to be, potentially deadly for fish. A number of water changes will need to be done to safely get back to a normal range.
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86 ssinit

Well in my opinion and mine alone :). This whole nitrate poisoning is just something to sell product. I beleive this went main stream :))) with the pond guru selling bio-home media. His videos are believable. He’s selling round cut lava rock for a fortune. Great salesman!! The api master kit didn’t even have a nitrate test in 2003. I’ve got the kit :). High levels of nitrate are dangerous to fish on a long term. yrs! Thing that kills fish living in high nitrate is doing a major water change. This cleaning the water and changing the chemistry quickly. This kill fish. Blame high nitrates! Great way to also sell product. But if explained to people to change your water a little at a time over the course of a few weeks. Making the water changes larger as you go the fish would have been fine. They don’t push this fact. Fish can live there whole lives in high nitrate water without problems. It’s when the keeper adds new fish that these questions arise. The new fish die! They can’t handle the high nitrate.even if slowly acclimated they still die. The keeper than tests water and does a major water change and they all die. High Nitrates!!
For me I believe in clean water! I never test for nitrates I change the water in my discus tanks 50% 3x a week. These fish need new water. They need all the minerals that come with clean water. From this I’ve learned that all fish and plants do better in new water. So I recommend 50% water changes weekly for any fresh water pet! (Even shrimp). Do this and you can happily ignore all the nitrate talk :). And use sponge instead of bio-home media!!!
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