Quick Question

That depends on how it's made.

If the bottom of the tank is completely flat so that the whole base of the tank is in contact with the worktop, yes you do. Something like polystyrene tiles or a purpose made basemat. Even something as small as a grain of sand caught between the bottom glass and the worktop can crack the bottom when it's filled with water and heavy.

If it has a floating base, you do not need anything under the tank. A floating base is a rim round the outer edge of the tank bottom, usually where the side panels project below the base panel and often covered with plastic of some sort to make it look nicer. This type of tank will have a hollow under the bottom pane when it's on a worktop. With some makes you even invalidate the warranty if you put something under the tank.

I've been reading up on fish since I joined a couple of forums in 2006, and that's a lot of reading  .

Including a forum which has a member called TnTLondon.............