GE Silicone II is a much-improved product for aquarium use over Silicone I. Several years ago, GE added something called "bioseal" which they claim inhibits mold. I switched to "GE Silicone II XST", the white paintable GE Silicone that contains no bioseal. The Silicone II XST is extremely strong and adheres well to most materials including plywood, Acrylic, glass, cement, common silver heavy-duty tarps sold at Home Depot and PVC pipe.
When it is necessary to conceal something under water, I use small quantities of the GE Tub and Shower product with bioseal to repair Pacu chewed wiring, broken pump and filter parts and around water pipe fittings in my plywood aquariums. As the Silicone quantities with bioseal are small and the water volume is large, I am not aware of any of my aquarium fish having health issues related to the small quantities of bioseal.
I contacted GE and their response was something along these lines. GE Silicone products engineered for home use are not recommended nor warranted for aquarium construction. From their point of view, there is a huge liability issue.
Aquarium manufactures are able to obtain a clear Silicone product suitable for their needs. Someone might want to research this further.
See link below:
http://www.monsterfishkeepers.com/forums/showthread.php?t=113394&page=4