Yeap, I actually found that Liquid Nails makes a silicone alternative that is crystal clear. Works great for what I need, just takes FOREVER to harden such that the tackiness is minimal.
Its not for aquarium use, it was for something else. I got ahold of a beta light (tritium vial) and wanted to encase it in an acrylic tube for some ruggedness. (Beta lights are made from fragile class and will break, releasing the H3 gas and the light is done).
Works alright. A bit difficult to "inject" in the tube, but got the job done.