For freshwater aquarium applications, you do NOT want to calibrate the controller for 4.01 which is why they include the addedendum to the instructions and only include the 7.01 solution.
Calibrate the unit for 7.0 and you'll be fine. Quite frankly, I wish Milwaukee would simply change the instructions to alleviate this misunderstanding. Calibrating the 4.01 point widens the slope from what it would be with single point calibration and can lead to wider pH fluctuations than would be seen with single point calibration, and accuracy is best achieved by calibrating the unit as close to the set point normally used in the application.
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