I had this convo about 3 weeks ago, i did a lot of reseach and found out that Ge doesnt recommend any of there silicon's for home aquaium use,
Turns out they had a large law suit with a annomius puplic aquarium. something about a cheimical used in all of there silicon's for the harder agent.
I use permatex RTV, worked fine, i wish i would have saved that artical. i had the names of the chimicals that should not be in it.
but you can use bathroom stuff as long as it doesnt have antibacterial stuff in it.
i used a lighter on one side to hold the glass in place, but i had a local place cut the glass to fit for me, so all i had to do was wedge it in and seal it.
wasnt hard at all