There is someone on another forum saying that nitrate levels exceeding 20 ppm is dangerous to fish. That is complete rubbish. It's certainly good to keep your nitrate levels as low as possible but suggesting that fish will come to harm if they raise above 20 ppm is totally erroneous. You try and tell them but they just won't have it. I have done absolutely loads of research and you actually find different information on different websites. If you go to the aquarium pharmaceutical's website, they suggest that nitrate levels are okay up to around 40 ppm. Since they are a rather large company that manufacture numerous aquatic supplies, I have every faith in what they say.

I would never tell someone to keep their nitrate levels at 40 ppm, I like mine to be as low as possible, even lower than 20 ppm. But we have to be practical when giving advice. Some people's tap water comes out at 30 ppm. Telling them that their fish are going to die if it goes above 20 ppm is going to put the fear of God into them.

Sorta' like a mild argument about canister Filters and Bio Wheels ehh?

Nitrates
From Shirlie Sharpe,
Your Guide to Freshwater Aquariums.

The significance of nitrates in the aquarium is arguably less understood by fish keepers than the effect of ammonia and nitrites. Although nitrates are not directly lethal in the way ammonia or nitrites are, over time high levels of nitrate have a negative effect on fish, plants and the aquarium environment in general.

Effects on Fish
Fish will feel the impact of nitrates by the time the levels reach 100 ppm, particularly if levels remain there. The resulting stress leaves the fish more susceptible to disease and inhibits their ability to reproduce. High nitrate levels are especially harmful to fry and young fish, and will affect their growth. Furthermore, conditions that cause elevated nitrates often cause decreased oxygen levels, which further stress the fish.

Other Effects
Elevated nitrates are a significant contributor to undesirable algae growth. Nitrate levels as low as 10 ppm will promote algae growth. Algae blooms in newly setup tanks are usually due to elevated nitrate levels. Although plants utilize nitrates, if nitrates rise faster than the plants can use them, the plants can become overgrown with algae, ultimately leading to their demise.

Desired Level
In nature nitrates remain very low, generally well below 5 ppm. In freshwater aquariums nitrates should be kept below 50 pm at all times, preferably below 25 ppm. If you are breeding fish, or are battling algae growth, keep nitrates below 10 ppm.

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In my personal aquariums, the Nitrate levels are generally undetectable and for years I do not remember recording or seeing a test result positive for Nitrates. That just means the level is so low (good for me and good for the fish) that it doesnt register on the test kit. JJ

And besides, this is the only Oscar site I visit, nor feel I will need to visit....

I think we are quite alike. We actually research the subject before getting into a debate about it. There's nothing worse than getting it wrong. Problem is, everybody has their own opinion and most people don't like backing down, especially when lots of people are watching. I don't think we were arguing about the canister filters. You know more about them than I do. I have never used one and I haven't really looked into them at all.

Well quite honestly, part of the problem was uncovered when it became clear that many common products offered over here are not at all common over there where you are.

Too bad you didn't catch the good Queen Mother before she left the States, maybe she could have packed a bio wheel in one of her "hat boxes" for you. You know what the Queen has in common with the President?
(absolutely nothing.) Thats one up for you!

I agree completely.

Having run my own forum for a while, I've seen it time and time again. I love fish forums, but one of the downsides is the inaccurate information you can get. As you said, it's ALWAYS smart to do your own research.

Having successfully kept Discus before (spawned) - and they are the most sensitive fish I've ever heard of - I can beyond a shadow of a doubt agree that 40ppm is no biggie. Obviously, you aim for as close to zero as possible, but 20 to 40ppm in and of itself doesn't cause any damage in the short term.

Bottom line is...you just can't reason with some people. There are a LOT of people on this planet who are incapable of ever being wrong. I just try (unsuccessfully) not to let them get to me.