All Glass Silicone Gel seals the aquarium airtight, preventing any leakage problems. Choose fromClear or Black silicone gel. This strong, waterproof silicone, used to manufacture new aquariums, is now available for home use. This easy to use silicone gel tube has a twist-on nozzle for easy application and provides a long-lasting bond. It is permanently flexible and does not crack or shrink. It is non-toxic and safe for use on fresh or saltwater aquariums. Sealant cures in five minutes and fully bonds within 24 hours.
I love this stuff. It's easy to use and so versatile even outside of the aquatic world :)