In addition to what Big Dave said, and I agree with it all, you don't need to change the sand. The only time sand needs to be changed is if it's really gunked up from something like a Baq conversion or filter additives that have rendered it useless. Before you go to that much trouble and expense, you need to get a pressure gauge on the filter--that will tell you (us) a whole lot more about whether the filter is operating properly.

Don't buy the calcium, and don't buy into the "chlorine lock" philosophy--they're equally useless in your situation!

I'm sorry for the loss of your Grandmother...

Janet