I wouldn't use any non-aquarium chemicals. The silicone can adsorb them and later leach them into the tank--not good. A razor blade to get it started, and if it's acrylic paint it should come off pretty easily.
okay so now which skimmer should I use? I want one thats worth the money but not too expensive. Prisms? Seaclones? Backpacks? Berlins? any other suggestions?