steve wrote:Silicone only sticks to certain surfaces and material. If you're not sure, ask or try it out on a small test area.
+1
devilduck wrote:You can also use cyanoacrylate aka crazy glue. Dries instantly in water and is aquarium safe. Downside is that it doesn't stick to everything and turns white underwater.
+1 If you go with super / crazy glue... get the gel for gluing under water. The regular stuff is too watery. Most every dollar store has super glue gel.
Another option is epoxy putty. It's also aquarium safe when fully cured. Most fish stores will carry epoxy putty - usually the two little fishes brand. It's over in the saltwater section as it's used to secure coral to rock or plugs. It comes in a few colors so you might get a match to whatever piece you're working with. A less expensive option that's still aquarium safe is hardware store epoxy putty. Aquamend or loc tite brand are available at most home improvement stores for cheap. The downside to these is they are usually blue or white.. not much color choice. They do however hold much better than superglue and can still be used underwater.
Yet another option is JB weld or JB qwik. It's another two part epoxy that bonds to most surfaces. It's the strongest bond of anything mentioned in this post but it cannot be used under water until it's fully cured. It's a dark gray / black color and it's aquarium safe once it's fully cured. JB qwik cures much faster than regular jb weld.