Scum lines are exactly what they sound like: lines of scum that form around the water’s edge, adhering to tile, grout, gunite and even stainless steel. By scum, we mean carbon-based bather waste (such as body oils, sweat, grease etc.), as well as body products (like deodorant, perfumes, sunscreen and lotions). If you are unfamiliar with scum lines, ask any lifeguard. They are often assigned to scrub them off with a brush and cleaning gel, and it takes a good bit of time and labor. Not to mention, a lot of cleaning products.
Even the Cat in the Hat struggled with one in the bath tub.
Once scrubbed off the walls, a typical commercial pool gets a few days of a clean look…before the scum line returns. In reality, the scum adheres almost immediately after scrubbing, but takes time to build to the point of needing to be cleaned again. In other words, scum lines are an almost-guaranteed nuisance in a pool or spa. But why?
We can start with the physical properties of this 'scum' we refer to. It is primarily carbon-based and oily. And if we remember science class in 3rd grade, we know that oils are lighter than water, and float. Therefore...
Scum combines with dirt in the water, due to the sticky nature of its makeup. Often times, scum is less dense than water—depending on the chemical ingredients—which makes scum float to the top of the pool or spa. In fact, in some cases, carbon waste can emulsify (stay mixed) with the water when the pump is operating, and only floats when the water is over-saturated with it. A good way to detect this condition is to turn off the pump and wait.
After 15 minutes or so, look across the surface of the water. The surface may look dull, or you may even see chunks of scum. If not, turn the underwater lights on.
Chlorine struggles to accomplish complete removal of organic waste, which we at Orenda have discussed in great detail here. This is not to say chlorine cannot do the job in high enough doses, it just takes a lot, and we believe that regular use of natural chemicals like our CV-600 and CV-700 catalytic enzymes is a better, targeted solution.
Scum lines are evidence of overloaded pool water
Scum lines are an indication of overloaded water, where chlorine cannot keep up with the bather waste (oxidant) demand. If you have scum lines, chances are your water also struggles to reach breakpoint chlorination. They are very common in commercial pools and private hot tubs, and should not be ignored. No, scum lines themselves are not what is harmful. They are evidence of a bigger problem: overloaded organic waste and dirt in your water. If chlorine were able to keep up with your organic load, it would be almost impossible for scum lines to occur.
The bigger problem is not what forms scum, but what can be contained in it. Scum, because of its physical characteristics, can hold bacteria and disease in its blend. It's kind of like how algae can hold ortho-phosphates within their cell walls, protecting them from chlorine. Much of the bacteria is isolated from the sanitizer when that happens; this protects bacteria and disease from chlorine. The same thing can happen in the filter and the pipes.
We at Orenda recommend a regular, proper dosing of our CV-600 enzymes to help break down and digest non-living organics. That way, chlorine doesn’t get used up on the organics, and the path is cleared for chlorine to kill germs. Orenda products are natural chemicals that do not kill or oxidize anything, but they do a remarkable job of removing scum lines directly, as well as preventing them from forming. They are all natural chemicals to help you keep your pool clean and clear.
Layering of calcium and scum
Sometimes a scum line is not just organic waste, but calcium scale as well. Even if the LSI of the water is balanced, if a tile line gets hot enough from direct sunlight, water can evaporate quickly, leaving behind some calcium deposits. We call this the wet/dry effect. It's a fancy term for rapid evaporation.
When water rapidly evaporates and leaves behind some calcium carbonate, it's usually not a big problem. Sometimes all it takes to remove it is some SC-1000 and maintaining LSI balance in the water. However, if there is a layer of organic scum over it, that makes it more difficult to clean. Some pool pros call this the peanut butter and jelly effect. While not as fancy as "the wet/dry effect", the peanut butter and jelly effect basically means sticky scum covers calcium and vice versa. One shields the other, and it becomes harder and harder to clean.
Related: Carbonate Scale Removal Procedure
Fortunately for you, the Orenda program addresses both conditions. Either preventing the problems with CV-600/CV-700 (for bather waste) and SC-1000 (for calcium), or a direct cleaning process with CV-Tile & Filter or straight PR-10,000 on a rag. Here's a video showing a commercial sand filter with 10 years of layered scum and calcium on the walls:
And here's a video of a similar filter, using just PR-10,000 on a rag:
Scum lines are an indicator of water that is overloaded with bather waste. When combined with too high of an LSI, carbonate scale can combine with the scum line, making it even more difficult to clean. This is especially common in commercial outdoor summer pools, like community centers and HOAs. Neighborhood swimming pools are loaded with people wearing sunscreen and tanning oils, and the direct sunlight on dark tile also invites carbonate scale to occur.
Orenda pools do not have either problem, because of our proactive procedures and maintenance behavior. If you have a scum line and you need it cleaned quickly, consider our tile cleaner or phosphate remover to remove it. But as always, prevention is the easiest method; otherwise the issues will come back.