25W is the upper end of the wattage range for those coils as far as I remember.
Lowering the wattage is of course an option to prolong the coil's lifespan, as is switching to a juice that's less sweet.
You could as well try a higher PG ratio or dilute the juice with some distilled water to prevent dry hits and gunking, but then you'll most probably get massive spitback issues. At least I did.
Btw, the Cubis is very susceptible to environmental changes like outside temperature and air pressure. All tanks are in a way, but from all the tanks I've used so far the Cubis is king in that category.
I'm sorry, but the Cubis is a very badly designed tank that is known and hated by many for its coil issues, and although you may not want to hear it, but in the end it's better to just get a new and most of all better designed tank. It'll not only save you a lot of nerves, but in the end a lot of money as well.