What is the most common mistake people make when backwashing a DE pool filter?

The most common mistake is forgetting to add fresh diatomaceous earth after backwashing. A backwash dumps all the old DE, so if you go straight back to filtering without adding more, your filter is useless and your pool will go cloudy fast. Measure the right amount (usually 1 pound per 10 square feet of filter area) and pour it slowly into the skimmer while the pump is running.