thanks.
actually I have never had a tank leak. the tanks I had at my parents lasted from the early 90's (the 30 gallons were from about 1990, the larger tanks from 1993 and 1994) all the way to 2008 with no issues.
if a tank is bought new, set up on a good stand, and not drained down and moved, it should go 20 years I would think with no issues.
its when you start draining and filling, letting the silicone go dry etc that you really increase the risk.
with this big tank, just because of its size, I will probably replace at the 15 year mark, just to be extra safe. this much water can potentially do a whole lot of damage..