If you have a phosphate level AT 125ppm, as I do, based on the Taylor kit reading, would it be worth a dose of Phos-Free to try and lower it even more? If, as you say, there are seemingly many more sources of phosphates, why not try to get it closer to zero (or at least below 100 since I doubt zero is realistic) to give you a buffer zone should your city water add it during normal fill-ups from evaporation or from regular chemical morphing into even more phosphate stuffs.