So, what causes the silicone to start leaking? The tank is about 10 years old. I'd like to avoid this with other tanks.

How long have you had the tank up for??
and has the tank sat empty at all ever??

there can be a few cause for it to leak.
#1 unbalanced stand
#2 being moved with water[like half full]
#3 being bumped while being moved.
#4 quality control[lack of] when being built.

Tank has never been empty except when it was moved, twice. Last time was about 1.5 years ago. Only empty for a day or two. Tank has been up for about 9+ years.

I have torn down and wrestled the tank outside. I cleaned and filled it with water and have found the leak while scrubbing the silicone with a toothbrush. There is a leak in the back left corner about 3-4" up from the bottom. Can I redo this spot/side or do I need to redo the whole tank? :frown:

you might get some advice to just do that side but no, it has to be done completely IMO. you could get away with stripping all the inside seam and redoing it all in one shot but the seam inbetween your panes of glass is the one that holds the tank together. I'll quickly explain, when I built my tank and other companys build theres they first put silicone on the glass edges and sqeeze them together real tight! this is your actual bond of strength. sometimes theres lots of silicone squeezed out so you can run your finger all along the inside of the tank to get another seal so to speak. some builders will just let the tank dry and cut out this excess,then do an inside seam of silicone[the method I like]

Richer,

Am constructing a terrarium at the moment and sent DH Chris to the store to get Silicone I. However, when he brought it home the package says it's the Kitchen and Bath stuff and not the Door and Window stuff. Silicone II must be the Window and Door silicone, don't you think?

The kitchen and bath stuff apparently has a mildew resistant in it which is toxic hence the reason one doesn't want to use it. I couldn't ever find Type I but I used 1200 successfully.

http://www.crlaurence.com/ProductIma...ant_587_th.gif

qUinn,

Couldn't find the GE 1200, but did find that Rona carries a product for use in aquariums. Product #2401-5426 Rona Window and Door Clear, $3.69. No other colour than clear, though.

The 1200 series adhesive is actually stronger than the regular silicone. It's what SeaStar uses in all their tanks.

Yes that makes sense as I believe it might have been Inter-American who recommended it to me, as they gave me half a tube of silicone once as well. I expect those in the manufacturer business all use the same brand.