Earlier on I had mentioned that I thought Carts were preferred by PBs in part because of ease of installation.

I am no expert on DE filters so I'll certainly yield to your superior experience and that of other owners.

Your reasons for changing sand are pretty much the same as mine--when you have to, but not before.

But if the filter requires repair and the sand removed to make the repair, I would be leery of re-using the sand. I suppose it could be OK, but new sand is pretty cheap--200 lbs is between $20 and $40.