Quote Originally Posted by Tom Highum View Post
I have heard that it costs a lot though'
It is really not all that expensive unless you need to reseal an entire aquarium.

Quote Originally Posted by John View Post
Works fine for me and worked fine for me all day. I can't explain it.

Johnny where do you buy the DAP silicone?
DAP brand aquarium silicone is available at just about every hardware and do it yourself store in the US.
For small projects like this and general tank repair the 2.8 fl oz size is perfect. For about 5 dollars you can do multiple small projects or reseal an entire US standard 10 gallon tank. The small tube size is better than caulking gun sizes as you get a better shelf life out of it if you only need a small amount. A standard caulking gun size has to be completely used within 72 hours of breaking the seal or it gels up. A tube will last six months if you close the cap, keep it in a ziploc bag in the fridge. (pro tip I got from an aquarium manufacturer in San Diego!)

I buy it at Ace Hardware online for a very very low price as I buy in bulk. (DAP product 688)
DAP has two different versions of the same product. They are identical in formula but different in packaging.(DAP product 688 also)

DAP does sell it in a caulking gun tube form, however after chatting with the folks in San Diego a few years back I have never bothered to order it.

You can also get All-Glass brand in the roughly 3 oz. size for about ten dollars at any major chain pet store. To be frank, it is an inferior product to DAP in my experience.

There is a few other brands of Aquarium safe sealant in the US, but I have not used them...yet

For a pretty good run down of Aquarium Silicone use try here.
(It is not nearly as informative as the chapter in my vivarium book-in-progress, but it covers the important parts.)