I've seen tanks made of the acrylic purchased at Lowe's - and they used the Weldon Glues to attach the panels to each other. Usually a very thin one and a thicker one are used to be sure to fill all of the gaps. (the lower the # , the thinner the Weld-on. IIRC you'd be aiming to purchase a 3 or 4 and a 6(correction - this should say #16)..but do check that information first!)
btw - Weldon is not the easiest product to find locally, best to google acrylic companies in your area. HD & Lowes do not carry it for some reason.
peter, also, for a cheaper price, you can have the panels made by Plastic Works on new Rochelle - will svae you a tone of time (and materials) in mistakes.
Plasticwork in newto is verry expensive. Maybe not so much for this size but definately woth looking into. They also dont sell the thick weldon or not since I was there a couple of months ago.
Thanks guys I haven't been working a lot lately because of school but i think im going to start working on it again this sunday. I need to get the weldon also.