Quote Originally Posted by JoshU
Yes, if the sand it 10 years old and it's already out of the tank you should replace it. Also clean off and inspect your laterals (fingers) at the bottom of the filter. Although you maybe able to go several years without chaning sand it's best to change it every 2-3 years for best performance.
I'm sorry, but I MUST disagree with the last part. As the sand gets older and dirtier, it actually filters better--the size of particles it catches gets smaller--a good thing. There is no reason to just change your sand every 2-3 years. I'm on year 4, Poconos (another moderator) is on year 9 with the same sand. Filtering just gets better each year.

I DO agree that once you empty the sand from the filter you should replace it with new sand. Filter sand is too cheap to save money there. Even when they charge $12 for 50# bags (a highish price) it's not a lot to pay to change it.