You only need to add more DE when you backwash/clean the filter.
Also, you only add the full amount of DE your filter calls for (6lbs for the 65, I believe) the first time you add DE for the season. After that, when you backwash, only add 80% (4.5 - 4.8 lbs) since all of the DE won't get flushed out when you backwash.