Yes which is why when I have around 30 fish in a 20 gallon, leave it for two weeks the nitrates are 7ppm... I'm lucky if I test each tank for nitrate twice a year. I don't really care how much the tank is producing, what I care about is how much nitrogen is going into the tank. When I moved here I tested the tap water then setup my tanks and never tested any of them for nitrate in the 6 months I've lived here till your last post. The filterless was 0ppm which I expected since there is basically no stock in there. My 20H with all ~30 little fish was 7ppm and the big 55 with its heavier stocking was around 15ppm. The 20 and 55gallon and high-tech so they get fertilizers. One of those fertilizers is KNO3, which is adding nitrate. High productive planted tanks are nitrogen sinks, they will usually demand more nitrogen then normally available.
You see it as pollution, which its not. Its just nutrient excess if its building up, its simply shows inefficiency IMO. It can be dealt with via water changes or you can use natural means(plants). I normally change 50% weekly regardless of levels on all my tanks. At home weather it was 40ppm or 0ppm in the tank it got a 50% water change with the 20ppm tap water. Thus I rarely tested and just accepted that test as a general idea of how the tank was functioning. Also I can't deffer red from red all that well from their silly color card.
After testing my tanks in response to your last post I got thinking. Basically I realized how nitrogen starved my filterless soil tank was, since I normally exclude it from dosing. So when I added nitrates to the other tanks yesterday I included it. I retested it just now and *poof* its got 20ppm of nitrates
. The way I view things it should be a much happier tank for now.
My parents well water has 25ppm according to lab tests and my useless API test kit at those levels.In the USA nitrate levels are limited to 44ppm so here it is well within the accepted level. That level is normal of it and has been consistent for the last 9 years. They run a daycare out of that home, we have to have the water tested since its a private well and it does pass drinking water standards. We use it as drinking water and always have. The natural springs down the road have the same nitrate level so its normal for our area. Also pay attention to what nitrogen is being measured, our water report is in Nitrate-Nitrogen(NO3-N) which is different from just nitrate(NO3-). Nitrate-nitrogen is limited to 10ppm in the US, so perhaps this is what you are talking about. However the API test booklet mentions it on the nitrate test page. Nitrate(NO3-) tests give readings 4.4 times higher then Nitrate-nitrogen(NO3-N) tests. Which is why the number on our water report is usually really close to 5ppm NO3-N. I only know this because I was once confused by the majorly different reports of the lab and my API kit, till I finally figured out they were reporting the same thing in different ways =/