Water Level

• The pool filter and motor are designed to filter water, not air. Monitor the water level of your pool, as swimmer usage and evaporation cause the water levels to drop below the skimmer at times. If there's not enough water to enter the skimmer, the pool circulation will decrease and may even damage your filter motor. The ideal level for your swimming pool water is somewhere between one-half and two-thirds of the skimmer's vertical height.
  
  

Baskets

• Empty the skimmer basket. This can easily get clogged and block water circulation, especially if your pool is beneath a tree that sheds leaves quite often. After a heavy thunderstorm where twigs and small debris have found their way into your pool, the basket can get filled up fast. The pump basket that is connected to the skimmer via a pool hose must also be cleaned after vacuuming. This is where the vacuum debris is collected and resides. If too much debris is in the basket, circulation will suffer as well.
  
  

Backwash

• Backwashing a filter is the process of rinsing it clean of the dirt and debris it has collected over time by filtering pool water. Sand, diatomaceous earth and cartridge filters all have different methods of backwashing. The filter needs backwashing when the pressure gauge rises 8 to 10 lbs. per square inch above its normal operating pressure. Internal pressure increases because circulation is being blocked from too much debris and dirt inside the filter. Backwashing is the most common way of restoring water circulation.
  
  

Motor

• The water level is good, the filter has been backwashed and all the baskets are clean. If this is the case and the circulation of the water is still too low, then it can be a sign of a faulty or worn-out pool motor. The motor is what provides the energy and suction, pulling the pool water through the filter system so it can be cleaned. When the motor begins to struggle or wear out, it's not as powerful, which results in a drop in pool circulation.