How Dangerous Is It Not To Have A Level Tank?

[Stroker]

If the surface your tank is on is true to the tank there is no physical reason that will cause a crack. I learned a lot of physics when I got my divers license and there would be little to no difference in pressure on the bottom of the tank just because it was a little off level. The guy who had 4 tanks in a row break probably has something causing his base to warp. That is also probably a bigger reason for the Styrofoam as it will even the pressure if your stand isn't 100% true. I don't know maybe vibrations are an issue in some parts of the world but it would take an earthquake or just some real rough horseplay to disturb my tank.

 

[xxBarneyxx]

I would say if it is fairly easy to level it out then do it. I did have a 60g(ish0 tank that was about half an inch out from left to right that was up and running for about a year with no problems (wasnt a very expensive tank either).