sand change

I am going to change it my filter sand this year. My question is, should I change it before opening or after? Is it better to get the bad stuff out of the pool with the old sand, or use the new sand that 'should' catch more stuff?

My boss and I inherited the community pool from a long, long life of negligence. As in filter sand has never been swapped out and the filter never cleaned.... the bottom of the pool is crumbling apart, the chemicals were not kept consistent and had perpetually high chlorimines and dissolved...

Hey guys, first time poster, long time lurker ;) I have a commercial account with seven TR-140C sand filters, and they want me to change the sand in all seven. I told them sand doesn't need to be changed unless it's fouled up somehow, but they have deep pockets and they want it done. I'm...

Do any pool company out there use equipment to get the sand out of the filter that's reliable