Thanks for your post @Velxunai and welcome to Workshop. It's great to have you join the community. I hope you find plenty of useful information and advice here, and have some fun. I also hope a Workshop member can assist with your tank. Good luck with the project, and I look forward to reading about some of your other projects and plans.
Please let me know if you need any help getting the most from the site.
I would try something like silicone caulk. You would need to make sure you have a clean surface first, and maybe even consider roughing up the glass with wet/dry sandpaper to help it bond.
@Velxunai Selleys make a liquid nails construction adhesive that is specifically designed for mirrors, metal and glass.
Way cool Velxunal, & thanks for the heads up about the alluminium angle extrusion. I'm all about DIYers saving money, because that's how I've operated, & it's very rewarding to do a great job for the least expenditure, but without compromise.
How is this project going @Velxunai?
Be great to see some photos when you have a chance.