how to build a fish tank?

Checkout the DIY forum here--lots of links. I'm guessing this will end up there eventually anyway.

It's cheaper to build you own if you going really big--more than about 250. Smaller tanks, if you want them a custom shape. It's not hard, you just have to be patient. I wouldn't tackle it as a first time DIY project, unless you're fairly handy with a saw.
 
Do lots and lots of research before you start. Generally speaking, it's more economical to build the larger you get. But it's also more difficult. If you think you're handy enough to take on the project, my biggest tip is to make sure you leave it outside and filled for several days. You can't even imagine what 200 gallons of water would do to your living room.

Do a google search on DIY aquariums and you'll find a ton of info...if you have specific questions try out the DIY forum, you'll get more help there.
 
I will agree with what has been said about it being more economical the larger the tank. BUT, if you are like me and have happened to come across free glass, then it is worth a shot on a smaller tank.

I have personally made 8 tanks, ranging in size from 80 litres to 220 litres. The main thing you need to make sure of is that the glass is the right thickness for the type of tank you are building, and that you use a silicone with an "acetic" cure. The main thing you will need is a hell of alot of patience, don't rush it or else you will end up making things harder for yourself.
 
Or you can do like I did and use Acrylic. If you build a reef ready tank, you can save money with Acrylic, even on an not-so-big tank. The 75 gallon drilled reef ready tank I built cost me 155.00 for the Acrylic cut to size. The biggest savings I got though was in building the stand and canopy. My 2x4 framed stand cost me about 40.00 and is WAY stronger than anything youll buy at an LFS for 250+.
 
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