Originally Posted by BillD
I would think that any hardware or home improvement store would have some. Silicone's primary use is as a multi purpose caulk for buildings. The only consideration is that the silicone not have any mildewcide in it. Avoid any product that says "Tub and Tile" or "Kitchen and Bath".
So, because I am in the process of my 3rd strip/reseal use any silicone that says "aquarium safe when cured" the other brands can say "fish friendly or great seal with no toxic blah blah to fish..." My brother is a chemical engineer and explained that these things are pretty much all identical and in fact one story he told me was that of a "safest for fish" which degraded in less than a year. So, save some money and if you need more don't waste money with the little tubes- it keeps (top tightly screwed on no air, for 9+ months.
Good luck and and chemical questions like these can be answered by a guy that wears a lab coat in a secure location (how cool?) just ask!