I think being diluted in oxygen rich water that has strong flow, surface agitation and filtration such as a typical fish tank would be FAR more encouragement to biodegrade than being opened a couple times a week after sitting fairly stagnant…
Also consider that 24 hours = 17280 minutes… my 2 liter bottle (½ gal) treats 20,000 gallons… So for me to have my ½ gal bottle open for 24 hours collectively I would have to keep the bottle open for one minute per dose (it takes me far less than this) and would have to be dosing 1.16 gallons at a time…
I just don’t see even a gallon bottle ever being opened for any where near 24 hours… and I do not see a bottle of Prime ever experiencing anywhere near the amount of agitation, exposure to air or dilution that it will in even a few minutes in a fish tank…
Therefore, ignoring hype and viewing it from a matter of chemistry, I see how it is possible for Prime to biodegrade in our fish tanks in a short time where it would not biodegrade in the bottle allowing it a long shelf life.