From what I saw it seemed like you could just leave the PH sensor in the tank for long periods of time with out attention.
In very clean water, possibly, and even then the chemistry of the probe has a tendency shift over time. The surface of the bulb needs to be clean for a good measurement. On top of that I'm guessing you'll be growing algae... In my experience, you'll find yourself cleaning it about once a month( probably more in your case) and calibrating every week or so. It depends also on what the alga's tolerances are.
Also, this is not for fish. It's for algae.
I was gonna say, poor fisshies 