There are many factors that go into how often the filter needs to be cleaned. Most manufacturers recommend twice a short pool season
Backwashing will need to be done more often when the "load" is higher. Everthing from weather, rain, pool use, and type and freshness of the sanitizer enters into play. The other factor, if you are using a chlorine based sanitizer, is how high (or low) is your chorine stabilizer?
But...if you've had lots of algae growing weather (August is the biggest) and heavier than normal pool use, and as long as your filter pressures returns back to baseline after you break it down and wash the elements, I wouldn't worry unless it continues through the fall.