I wouldn't add stress coat to your top off/makeup water. Really no need for it. I'm assuming your using tap water that is why your using dechlorinator??? Sounds as if the API isn't quite accurate enough, you seem kinda "iffy" on the actual number results. Maybe a more accurate test kit might be in order or soething easier to read, or take a sample to your LFS and have them test it and compare the readings. Water changes with no addition of any chemical should bring in down.