Scum Lines, Biofilm & Inactive Enzymes: Pool Problems To Look Out For

As a Certified Pool Operator®, there are plenty of pool problems that you need to be prepared to address. In order to properly operate a swimming facility, you need to be able to quickly identify these issues and understand how to tackle them. Scum lines, biofilms, and inactive enzymes can all cause health risks that jeopardize the safety of swimmers. This article can serve to provide some insight for maintaining a safe and sanitary swimming environment at all times.

Scum Lines

The formation of scum lines is one of the easier swimming pool problems to identify and mitigate. A scum line is when deposits form at or slightly above the pool’s water line. These deposits are made from complex mixtures of contaminants with low water solubility. Some contaminants include calcium scale, skin fragments, suntan or skin oils, debris in the water, cosmetics, and detergents.


The pool surface above the water line can get wet from waves, splashes, temporary increases in the water level as swimmers enter the pool, as well as when the water level drops. The film of water containing contaminants can then evaporate, leaving behind deposits of chemicals. If you do not properly balance water chemistry, scum lines may be due to scale. Once scum lines form, they begin to attract other contaminants like algae and bacteria.

Fortunately, there are many pool cleaners that help prevent scum line formation. Make sure to select a product that was specially designed for pool or spa use, as some cleaners have ingredients that are not compatible with pool water. These ingredients, like phosphates, can actually increase the scum line. Like many pool problems, it’s best to prevent scum lines from forming. Regularly brushing the waterline and maintaining proper water balance is the best way to accomplish this.


Biofilm is one of the more challenging pool problems. Bacteria can protect itself from disinfectants by forming into a layer of slime called biofilm. It can take a disinfectant concentration 100 times higher than normal to kill off biofilm as it does bacteria suspended in water. Bacteria in biofilm secretes a plastic-like substance called extracellular polysaccharides (EPS) which acts as a protective layer around the cells in the biofilm and binds them together. Most human bacterial infections that occur at swimming facilities involve biofilms. They can harbor disease-causing bacteria that jeopardizes the safety of swimmers. A Certified Pool Operator® can combat biofilm formation through proper water balance, regular cleaning, and jumping on the disinfection process as early as possible.


Living cells within plants and animals produce proteins from strings of various amino acids. The cells form proteins into specific arrangements called ‘enzymes.’ Just like how we digest food and break them down into enzymes, pool and spa products use enzymes to break down contaminants in the water. However, these enzymes lose their structure over time and no longer serve their original function, which creates pool problems and hazards. Algicides, water, and oxidizers all speed up this process. Once inactive, these enzymes become protein contaminants that need to be removed.


Solving Pool Problems Like an Expert

To find out more about maintaining a pool properly, learn from the experts at Pool Operation Management. The CPO® certification class is a great start to becoming a pool expert. Pool Operation Management’s award-winning pool operator training courses show you how to properly operate a swimming pool or spa facility. Our two-day courses offer a wealth of information and training in everything from pool chemicals and energy conservation to risk and liability. For the very best in pool operation, contact us today.

*This information is obtained from the Certified Pool and Spa Operator Handbook. This information may not be applicable to your pool based on your pool type and location. One should reference all applicable regulations and standards for your facility.

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