Silicon melting?

[zoomin]

So I got an old 40g and siliconed in some baffles for my sump.

I used clear All Glass Aquarium silicon. I taped it all off and pulled of a satisfactory first time effort, IMHO - not pretty but totally functional.

The system has been running for about a month now, rock and sand went in within the last two weeks. No critters have been introduced except a few hitch hikers .

This morning I saw some whitish film floating in the display tank. Down in the sump, the silicon on the baffles has gone gooey and is starting to melt and float into the tank. It's starting at the areas that are really thin, as the joint tapers out to a very thin edge.

Where did I go wrong?