What Is Going on When the Pool Has a Film on the Top & Bubbles in the Skimmer Box?

Swimming pools require a consistent regimen of maintenance and chemicals in order to remain clean and clear. Occasionally, however, pool water chemistry suffers and water becomes foamy; or, in some cases, a thin film appears on the water's surface. These are both signs that the water's calcium hardness and sanitizer levels potentially need to be balanced.

Filmy Water

Most pools use chlorine as the main sanitizer. It's responsible for keeping the water free of bacteria, which helps prevent algae and other problems associated with a dirty pool. A film can form over the pool from a combination of body oils, lotions and dirt that build up due to heavy usage. This film can form also when the pool's filtration system doesn't operate correctly. To be effective, the filter needs to run for at least 12 hours per day to circulate chemicals and filter out dirt and debris.

Foamy Water Causes

The most common cause of foamy pool water is a drop in calcium hardness levels in your pool. This is more casually known as soft water. Another, more common-sense reason for suds in the water is due to cleaning products. Pool owners who are looking to clean the tiles near the water line or the vinyl liner of their above-ground pool use detergents that often leave suds on the top of the pool. The same residues that cause a film on the top of the water can also cause foamy pool water. One last, common reason for foamy pool water is the over-application of algaecide in the water.

Air in the Lines

A filter needs water in order to operate properly. If the filter does not have enough water going through the system, air enters the lines. Make sure the water is at least at the halfway mark of the pool skimmer's vertical height. Leaving the water lower than that can cause bubbles to blow from the return jet. This leaves a heavy foam-like appearance on the pool surface. Check the pool hoses as well for cracks that allow air into the filter system.


A film on the top of the water can be an early indicator of a sanitizer problem in your swimming pool. Immediately run the filter and shock the swimming pool, because it's likely that the water is becoming cloudy if a film is starting to appear over the surface. To do so, add 1 gallon of liquid shock for every 7,000 gallons of pool water and broadcast it over the surface. Run the filter for 24 hours continuously. Anti-foaming chemicals are also available at pool supply retailers. These can be added in conjunction with the reinstatement of proper water chemistry levels.