Yes, any of our B-12 Chemtool family of gasoline fuel additives should be compatible with the previous fuel treatment. The suggested frequency of use depends on the product; part #0116 in the metal can, for instance, is recommended every third tank but is actually safe for use as often as desired. As for longevity, these additives will retain their effectiveness for at least a year in sealed tanks. In open tanks, their efficacy depends on numerous factors, including fuel system configuration, temperature, humidity, type of gas, and fuel level.