Pool filter channeling - causes, symptoms, and how to fix it

May 30, 2017



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Filter Channeling is a problem

Seasoned pool operators know the triad of great pool water: filtration, circulation and chemistry. Without effective filtration, there will always be problems... and filter channeling undermines filtration.

Filter channeling is a condition when water finds its way through pockets in the filter media, and avoids being filtered. Water finds the path of least resistance, so if it can form a channel for easier flow-through, it will. A common form of filter channeling is when water seeps around the edges of a sand filter tank, avoiding the sand bed almost entirely.  This is especially evident in pressure sand filters after backwashing.  You can see pictures and video of two examples in this article.

Symptoms of channeling

Abnormal Backwashing Cycles

If you're backwashing often without a noticeable change in pressure...or the water being wasted looks 'okay', it may be a symptom of filter channeling. These problems are often caused by heavy organic loads building up in the filter sand and clumping it together. If not just organic loads, calcium can harden in the sand too, as well as polymer-based pool products, aluminum and phosphate removers. Regardless of what is causing the sand to clump together, breaking down those clumps and freeing the sand can alleviate a channeling problem.

Cloudy Pool Water

Another symptom of channeling is cloudy pool water. If water is able to sneak through a filter without flowing through the sand bed correctly, more particles can get through without being filtered out. Of course, cloudy water alone does not always mean your filter is channeling, but it may be worth checking every once in a while.

Ridges inside the filter, around the edges


 Ridges will form around the inside edge of a filter if it's channeling water around the tank.


If you suspect you have channeling, shut your pump off and look in the filter. There could be pockets through the sand (a  channel), but more likely, ridges of raised sand form around the inside edges. These ridges indicate water is going around the sand bed along the sides of the filter tank itself, and form during backwashing.  The middle of the sand bed, in this situation, should look fairly settled with lots of debris on top.

How to fix a filter channeling problem

Understanding what causes channels to form is the first step: the sand is getting clumped together somehow. Pool operators can "un-clump" the filter sand, and that may fix the problem right there. Operators, service techs and staff can look at a channeled filter, but it still may not be evident exactly what is clumping the sand. Non-living organics involve themselves in filter problems in almost every case. They may not be alone in the clumping effort, but they're almost certainly part of it.

If your pool has high calcium or evidence of carbonate scale, calcium could be part of the problem. If you use polymer-based products like clarifiers, those polymers can contribute to the clumping too. So can aluminum-based products like certain types of phosphate removers (fortunately, not ours).

We recommend doing a deep clean/purge of your filters with our enzyme and phosphate remover and see what happens. It's an affordable way to remove organic contamination and refurbish your sand.  If a channeling problem persists, it will be easier to problem solve once you get those non-living organics and gunk out of the equation.

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