You don't solve algae issues by vacuuming. Sounds like someone in business in your area has a service they want to push, even when it's not the best way to do things.

If you have a DE filter, there's no reason why your pool shouldn't be pristine all the time.

Post all of the following:

+ Your pump run time (24/7; 6 hrs/day, whatever)
+ Your free and total chlorine levels
+ Your pH
+ Your stabilizer level
+ A list of the chemicals you've used this year.

Best wishes,

Ben