coffee table glass is likely to be tempered glass for safety just so you're aware. on the plus side, that makes it stronger than plate glass. But they don't chip/crack gracefully, they shatter catastrophically, if hit hard enough or in the right place (ie on an edge) to break. Many people use it though. 1/4" tempered glass can support quite a bit.ftrsb3 said:Another question, could I use glass from an old coffee table if the thickness is more then 1/4 inches?
depth of water is the most important factor in glass thickness, followed by unsupported length. Depth is what determines the pressure on the glass. doesn't matter if the tank is 3" wide or 3' it would need the same thickness. So if your reclaimed glass is used in the same depth of water and supported in the same places as the tank it came from I'd say it'd probably be fine. But do your diligence and google for some aquarium glass thickness calculators, they're out there.
Also the larger of your proposed tank dimensions is only about 35 gallons. You can get a 40g from petco right now for $50. The material to build a plywood tank that size is likely to run into the $100's. So not economically worth it to make small plywood tanks really. Even for trial/practice I wouldn't bother. Speaking from my own thoughts/experience because I want an 8 footer in my basement and I'm not sure I can maneuver a full glass or acrylic tank down my stairs, but I can build a plywood box in place and get an ~8' sheet of glass down for sure. I haven't considered building a smaller practice tank, I'm just going to go for the big one when the time comes. I've been building it in my head for 10 years .