Originally Posted by bahamut285
I would agree with prodrumernate. Make one tank, put it in the sink and fill it with water after it sets and leave it for a good few days (a week maybe) to make sure it doesn't leak or explode.
Also "gluing together some plexiglass/acrylic sheets" is not as easy as it sounds, there is some physics behind it. I believe it has to be a certain thickness depending on the HEIGHT of the tank.
Thickness is not really an issue with acrylic. It is not glass it will not explode or crack. What you will have is bowing if the length is too long. This is easily fixed by adding cross braces on top section to add strength. This is done to some glass aquariums that use thinner glass to prevent bowing, cheaper production tanks. As a rule of thumb 12" high can be made with ¼" acrylic; up to 18" with 3/8" and up to 24" with ½". The original poster wants to do half gallon tanks so its not even an issue.
You want to weld the two pieces of acrylic using the acrylic glue, Choloroform or Methylene chloride. You put the glue in a syringe and you run it along the seem of the two pieces. Capillary action will suck the solvent between the two pieces. You might want to smooth down the edges with some sand paper but do not over do it or you can create uneven surface or round the edges which will make for weak joints. You cannot move the 2 pieces of acrylic at all at this point. It takes about 12 hrs to set.
Use 5 ml syringes with 18 gauge needles. These should be bought separately because the syringes usually come with 22 gauge needles. It is recommended to use glass syringes.
So check and see if any of the solvents your about to buy has methylene chloride if it does you should be ok. The stuff is very thin and should be able to wick between the two pieces.
If I was gonna build something that small though I would probably go with glass as it would most likely be the cheapest route. Also you could use a heat gun on low and slowly bend the acrylic into a box shape reducing the number of seems you will have. So just top bottom and then the one side seem. If your really creative you could make it out of a single piece of acrylic using the right cuts and heat.