Quote Originally Posted by Mwil3 View Post
I would think that as long as your tank isn't cracked it would last forever. You will need to replace gaskets from time to time and they say that the sand should be replaced about every 3 years or so. Replacement parts are much cheaper than a new unit (especially if you "know" your system already.) You can even get a new gauge and you will feel like a you have a brand new filter.
Your sand NEVER needs to be replaced unless you've gunked it up with Bacquacil or something equally bad. I've been using the same sand for 9 years, and my fellow moderators have been using theirs for longer and shorter amounts. As the sand gets older and dirtier, it filters better than it does when "new" (remember: your sand is far older than you are or will ever be).