You can find it at any hardware store. Some will say not safe for aquariums. As long as it's 100% silicone with no additives, it's fine. One particular GE tube will say not aquarium safe, however it's totally safe. This is put on the label for proprietary reasons. GE makes silicone that's packaged as aquarium sealant. They make this for another company. The contract with the other company requires GE to put not safe for aquariums on their tubes. I used to manage a hardware store and was given this lil' tidbit personally by a GE chemist and sales rep.