Just had a quick look the telly is W x H x D 79.5 x 48 x 48 cm
not including stand, and the overall weight is 42 k. If you wanted to fill the space with a tank, lets say the size of the screen which I will guess approximately 60cm wide? I will assume that the tank is 10 cm short of the top to allow access (although this not really enough) so that would be W60 x h38 x w48 which would be about 110 litres. 1 ltr of water weighs approxinately 1 kg you can see that is over twice the weight of the original set!
You could always go for something like this...