Silicone doesn't 'glue' things together well... Except for glass. Any kind of superglue (cyanoacrylate) is aquarium safe, and you should very easily be able to get aquarium safe epoxy (in your LPS/LFS saltwater section). Actually, I gave up on aquarium safe epoxy, I just use whatever type of epoxy I have around (Have not had a problem yet) runs about 1/4 the price of the aquarium stuff...
Andy