Now I am well aware that this all might seem like an example of spending too much time on fert dosing. I look at it another way. I was dosing very, very rich levels for quite a long time, and was reasonably successful (by my standards!). One thing that has never changed is taking light, CO2, and maintenance seriously. IME, get those right and you have a lot more leeway to monkey around with fert dosing.
Interesting that you mention this...
So, for the last few weeks I have been lowering the KNO3 dosing in my 75g and, to a lesser degree, the wifes 40g tank. For this week I was dosing 17ppm KNO3 total, down just a little bit from the 30+ that I used to dose. So, just for grins I test the NO3 level in her tank and my tank tonite - to my surprise both test tubes were still pretty red. Not dark red, but red enough. Decidec to test the tap water as well - get a light orange. So, the API test solution must be working to some degree.
Looks like I will be headed even lower over the next few weeks