When is it necessary to change sand?

[debdevero]

We have a 30,000 gallon ig pool in MI. It is 10 years old. The sand in the filter is the original - and have heard from several sources that the sand becomes too fine should be changed. The filter seems to be working fine - however there is debris in the filter ( leaves, etc) that I plan to remove. I would like to hear how others maintain their sand filters.

[CarlD]

I'm going into 6 years with the same sand. Poconos is at 10 or 12. The only two good reasons to change sand that I know of are:
1) It's gummed up with something, usually a chemical we recommend you DON'T use, or from a Baquacil conversion--that gums up the sand requiring change.
2) It's so badly infested with algae it's constantly re-infecting the pool and you can't get enough chlorine in to kill it--the new sand is probably just cheaper.

Two less good reasons:
1) You want to go to Zeobrite, or whatever it's called. Weighs less, far more expensive but it's supposed filter finer. However, adding DE will clog it where it won't clog sand. You have to use the DE replacement rather than DE if you add DE to your sand filter.

2) Somebody tells you sand wears out. Sand filters better and better the older and dirtier it gets.

However, sand is cheap...I've been seeing filter sand on sale for $5/bag of 50# bags. That's $20 to change the sand in a 200# filter. Even at $10/bag it's only $40. It doesn't HURT to change sand, other than you lose all the added filtering qualities of old sand, but it doesn't help either unless your sand is gummed up.