i heard that plastic aquariums are bad for the fish as it releases something toxic in the water
Plastic, along with glass and arcrylic, can be used to build aquariums, however plastic tends to be used on things like 'Critter keepers' or the small plastic aquariums that you see in pet and aquatic stores. For most applications, glass and arcrylic are the safest options and can hold the weight of the water in larger tanks providing the material is thick enough.
all large tanks are made of acrylic, and the fish are fine. all tanks with curved surfaces are made of acrylic, too.
Depends what type of aquarium? Marine, Fresh Water or Tropical freash water?
As long as you use marine-safe acrylic, you should be fine as many manufacturers make plastic tanks. They are lighter and can be made into more shapes than a glass tank can. They are also less prone to breakage. However they can scratch easily and as such are a bear to keep clear. Algae scrubbers, scrapers, and even some fish are known to scratch the sides. But it can be done, the fish can be happy in it and no toxins will be leeched.
yes quite often aquariums are made of a very high stregth plastic the difference with this and glass is that the plastic can scratch but it is lighter and can be shaped and formed. alot of custom tank builders use plastic to come up with all kinds of wierd and wonderful shapes and sizes of fish tanks and no the plastic used is, like glass, definately inert, it will never leak chemicals or toxins into the water