Stock solution concentrations?

• pH: 6.8
• Temp:
• KH: 5
• GH:
• NH4:
• NO2:
• NO3:
• PO4: 1.75
• Iron:
• Dosing: 5 mL Flourish, 20 mL iron chelate (2 ppm)

Notes:
I had expected the phosphate levels to be less than 1 ppm, since I had dosed only 0.75 ppm to yesterday's phosphate levels of 0.2 ppm. What does that mean? Maybe the tests are inaccurate. I use SeaChem for the phosphate tests, and those colors can get tricky to gauge. Although I do calculate stock solutions based upon my 60 gallon tank, even though, there is probably closer to 50 gallons of water in the tank. Maybe I should adjust for that instead. Then I would have dosed 1 ppm of phosphates.

To adjust for 50 gallons of water, dosing would change so that:
5 mL KH2PO4 = 0.2 ppm (instead of 0.15)
5 mL KNO3 = 1.25 ppm (instead of 1.0)