I think it's do-able. I'd remind you that you're S.O.L. if a joint isn't done right and fails when it's full of water, where-as store bought tanks usually have quality control checks so that doesn't happen, but if you're still willing to give it a go, come up with a design for how you're going to do your bracing and what thickness and yadda yadda yadda, post them on a few reef forums like this one and you'll get some good feedback as far as if your bracing is strong enough and whatnot.
Edit: Also, daaaaaayyyyum, that's almost 480 gallons.
EDIT: yea i no my dad wants to make a sweet as tank in the basement he worse than me!
1/2" at that water volume is not thick enough acrylic, your looking at massive amount of welding and your going to have to do a brace ring around the top, im getting ready to build a 300 and in all honest.... your looking at something you need to be VERY experienced in acrylic to build and your looking at very expensive aka probably 2k in materials to build and thats being conservative
I think it's a very realistic goal, and that guy covers exactly what I was suggesting, which is making sure your bracing is big enough, if you make a solid top with the access holes cut out like he suggests there should be plenty of meat to hold it together (as long as you don't go crazy with your access holes).
I would certainly practice your acrylic joining with some scrap pieces of 1/2" so you can make sure that you can glue long corner joints and such without bubbles or other imperfections that could cause it to fail.
It all boils down to how confident you are and how much time you're willing to spend. I think if you get some scraps and practice for a couple hours, you could probably have it down pat and throw together a good aquarium.
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