In a running tank with fish that where the biofilter has finished cycling, the keeping of NO3 weekly records can help any beginner become more familiar with good water changing and filter maintanance habits and how to judge the feedback. It should always be remembered that NO3 is a "flag" test, one that tells about other things we are not measuring (there are hundreds of substances we want to water change out but NO3 just happens to be easy to monitor our progress or lack of progress.)
A rough guideline that we use is to hope that NO3 will hover around 15 to 20ppm -above- whatever our tapwater NO3 level is (as a sort of max.) It is really the trend that is more important to watch - we want it to hover around, not steadily increase or to turn up very high because we did nothing for a long time. As far as NO3 itself is concerned, its toxicity varies wildly with different species of fish. Some species can tolerate 400ppm and there are even reports of river catfish surviving in 1000ppm. On the other hand there are fish like German Blue Rams that some feel may get sick and die at less than very low levels of nitrate.
For the student of basic fishkeeping skills, which is what our subforum is all about, the really important lesson is how those gravel-cleaning-water-changing and filter maintenance skills play in to healthy tank keeping and how the NO3 test is our friend in getting some feedback while learning those skills (after one has the skills, NO3 tests are less often needed!)
~~waterdrop~~
