Why is DE coming through my skimmer and main drain, when the pool pump shuts off?
The cause of DE plooms coming from the skimmers and main drains is different than the type that causes DE to flow from the return jets. DE leaking from the return jets can be caused from a hole in the DE grid, or crack in the manifold, something like that. DE leaking from your pump, skimmer or main drain is likely caused by an air leak. Basically, when the pump shuts off, air enters the system, or water drains out of the filter and back into the pool. That’s when you see the DE go back into the pool from the skimmer main drain. The leak could be on the pressure side or the suction side.
With the suction side, the main symptom is pump priming issues. That means, when you turn on the pump it takes longer to prime or does not prime at all without assistance. Another common symptom is are bubbles flowing from the return jets. To check for air leaks, from compromised PVC glued joints in your Tees, elbow joints, and valves. Read our guide on finding air leaks here: How to Identify and Correct Air Leaks. We cover how to check your pump strainer lid o-ring, pump unions, and water levels.
Anything on the return side of the pump is considered the pressure-side. Common air leak culprits on the pressure-side are the pool filter’s air relief. If it is loose, you may see a water leak. Leaking unions on salt cells are a bad sign because when the pump shuts off again you are going to lose all that water out of your system. It’s going to run back into the pool.