Fuel gelling is caused when parafin molecules get cold enough to stick to each other.
This temperature is known as the "cloud point" because the fuel turns cloudy looking as the molecules start to stick together.
Anti gel treatment surrounds each molecule of parafin with a coating that keeps them from adhering to each other.
You must surround these molecules with anti-gel BEFORE they start to stick together.
If the cloud point is reached before treatment, and molecules are starting to form wax, you cannot unjell that fuel without warming the fuel to above the cloud point. Then, the anti-gel can surround each molecule.
The best procedure is to add your treatment before you fill your can, then add the relatively warm fuel from the underground tank. If the fuel has been exposed to cloud point temps, treat it, then bring the can into a warm place until the fuel gets above the cloud point. You could safely figure that 30* F would be the cloud point. Cloud point can be somewhat lower, like 18-20*F