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 may need to be balanced.

Boy playing in swimming pool.
credit: Flikr Creative Commons
Ideally, a swimming pool should have crystal clear water. When foam or a filmy surface layer appear, it needs to be treated.

Filmy Water

Possible causes:

  • Body oils or lotions in the water
  • Problem with pool's filters

Swimming pools use chlorine as the main sanitizer. This chemical is responsible for keeping the water free of bacteria, which helps prevent algae and other problems associated with a dirty pool. A film can form on the water from a combination of body oils, lotions, and dirt that build up due to heavy usage. This film can also form 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

Possible causes:

  • A drop in calcium levels
  • Cleaning products
  • Overapplication of algaecides
  • Air in the pool pump's water lines

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 cleaning the tiles near the water line of an in-ground pool, or the vinyl liner of an above-ground pool, may use detergents that often leave suds on the top of the water. The same residues that cause a film on the top of the water can also cause foamy pool water.

Another common reason for foamy pool water is the over-application of algaecide in the water.

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 level reaches to at least at the halfway mark of the side opening on the pool skimmer. A lower water level can cause bubbles to be generated from the force of the pool's return jet, which can leave a heavy foam-like appearance on the pool surface. Check the pool hoses as well, looking for cracks that allow air into the filter system.

Remedies

A surface 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 water—it's likely that the water will soon become cloudy if a film is starting to appear on 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.

Bulk container of pool shock chemical.
credit: Pool Supply World
Shocking pool water with heavy doses of chemical is a common maintenance task.

Anti-foaming chemicals are also available at pool supply retailers. These can be added in conjunction with the reinstatement of proper water chemistry levels.