Just for future knowledge....
You can pay way too much for a small, metal squeeze-tube of "aquarium" silicone from PetSmart/Petco...
Or, I forget if Lowes carries it, but at Home Depot, down the aisle with all the glues and like adhesives should be a squeeze tube of silicone. In the past Home Depot had 2 options, 1 that said aquarium and one that did not. What you're specifically looking for is 100% silicone. Wal-Mart might even carry it in squeeze-tube form.
Alternatively, if you want to invest in a caulk gun and use 10 oz tubes, look for either DAP brand 100% rubberized silicone (I only find it at Ace Hardware and a place called Elliot's Hardware) or GE Silicone I...not Silicone II, but Silicone I. GE Silicone I can be hard to find at times, but it should still be 100% silicone (SAME thing as aquarium silicone). Silicone II has mold and mildrew inhibitors in it and it supposedly is and isn't toxic to fish.
Edit...a Home Depot Link...
http://www.homedepot.com/p/DAP-2-8-o...0688/100128841
This is a 12 pack, but you get the idea:
http://www.homedepot.com/p/DAP-2-8-o...0683/205881786
Same here, just in clear:
http://www.homedepot.com/p/DAP-2-8-o...0684/205207319