No, I would not use a terrarium as an aquarium. Mainly because the bottom glass is not tempered(In Most cases, witch is most likely). Also, they use a different type of silicone witch is not resistant to a fully filed tank. Usually, on terrarium notice labels, it states to not fill over 30%(Commonly, between 10%-40%) because it can't hold as much pressure. You will also usually notice the glass is much thinner, measuring usually 1/3'' or more commonly 1/4''(55 gallon terrarium), whilst in aquariums, a 55 gallon would have around 1/2''-1''(sometimes more). I heard of people using it as aquariums, and they end up leaking after a few weeks, sometimes earlier and they end up ''exploding'' if I may say. Over all, I wouldn't do it.