So you were able to get some sort of liquid testing kit?
I'd post up the numerical results here for both your tap and tank water, just as a reference.
Nitrate(NO3) can sometimes be present in measureable amounts in tap water. Regardless, its often felt that if your nitrate levels hold at not more than about 10 or 20 ppm above whatever your tap water level is then your gravel-cleaning-water-changing maintenance is probably doing ok. Taking nitrate(NO3) readings is a common way of accomplishing a couple of common things that are not really directly about the nitrate entirely. First, its a sign of how the overall effectiveness of the gravel-cleaning is going. Secondly, nitrate(NO3) readings can also be seen as an "indicator measure" for dozens or hundreds of other trace metals or organic substances that would be too expensive or difficult for us to bother measuring in our tanks. Maintenance, primarily via the weekly water change and the monthly filter clean (or whatever ones custom intervals are for one's own situation) are really about keeping all these many "invisible" things under control so that they need not be worried about.
So Nitrate(NO3) itself may not really be a big danger (certainly not compared to ammonia or nitrite(NO2)!), as some species tolerate 100ppm or even 1000ppm, but hardly any hobbyist hoping to be a good aquarist would want to find NO3 levels that indicated poor maintenance habits!
~~waterdrop~~
