I bought a ultra low phosphorous checker. I was told that it doesn't matter if I use ultra low phosphate or ultra low phosphorous reagents. It'll still give me an accurate reading. So, I got ultra low phosphate reagents. I tested the tank before a water change. Was reading 200ppm, I panicked. So, I quick did the water change (65% water change) then waited a day or two then tested again. Still showing the same reading. Is it because I'm using phosphate reagents in a phosphorous checker?