fast setting something

[rossb]

why don;t you simpaly turn off your returm pump, drop your water level 3 to 6 inches (use a power head and a hearer in both the sump and the tank for 24 hours... then you can silicone it and not wory about anything..

exactly...I have drained the tank and applied the silicon..thanks for the tips.

Tony wrote

I'm sure I've read something once where wet silicone was used under water ... but I can't remember at all what the context was. Something about putting wet silicone on the glass, then scraping it off afterwards

Tony this is a good tip ... and I think it is what you are referring to. If you apply a bead of silicon to glass (like along a seam), and then spray the glass with water, and then smoosh the silicon in with your finger...the silicon will not stick to the wet glass but it will stick where the water isn't. When the silicone dries the excess will peel off very nicely (it is just about as good as masking tape)