Filtration: Clarified

Pool maintenance requires three fundamental elements: money, time, and frustration! Wait, no, that’s wrong…… checks notes

Actually a pool requires: filtration, circulation, and sanitation. 

As complicated as your pool may seem, if you take care of these three things, you will have a clean pool.  But we should talk about what that actually means in its individual parts. 

For this blog we will cover filtration. Filtration is the passing of water through a medium small enough to separate particles and debris from the water it is carried in. 

We start here because if filtration is not properly functioning, then there is a solid chance that the other two elements are messed up as well. For example, when your filter is dirty, water flow in the system is restricted and water does not circulate around the pool as well as it should. So solving for filtration might solve another issue. 

Filtration in the pool industry generally has three main issues, not enough ‘turn-over’, debris ‘bypassing’, or filters becoming ‘impacted’.

Turn Over

By ‘turn-over’ we mean how many times are we sending each gallon of water through the filter each day. For residential pools it is recommended to turn-over the pool at least once a day. For commercial pools it is required that the pool turn over at least 2-3 times per day.  When running a pump at 40 gallons per minute and multiplying for  60 minutes in an hour, a 20,000 gallon pool (about average size) needs around 8 and a half hours of run time. Running the pump less than this means we are not getting all the water through the filter each day.

20,000 gallons / (40 gallons per minute X 60 minutes) = 8.33 hours 

Bypass

When a filter has a bypass it means that there is a malfunction somewhere inside with the tank. Often it can simply be a part slightly out of place or missing. This allows water to enter and exit the filter tank without coming in contact with the actual filter surface. Similarly holes can develop on the filter surface itself. Whether a hole develops deep in a cartridge or a tear happens on the grids of a DE filter, water takes the path of least resistance and will find its way through those holes. This means we are not removing the particulates that we were hoping to filter out. 

Impacted

If a filter has done its job over a longer period of time it should eventually become full. At this point the material we are using as a filter no longer has room to accumulate any additional matter. This means it needs to be cleaned. If a filter is not cleaned in a reasonable time it will create a choke point, and starve the entire system of water flow. The cleaner stops moving, the heater may not work properly, we can’t run the solar, the spa jets don’t work, and all kinds of other issues. But most importantly, the pump cannot move water.  Leading to overheating and eventual damage to the pump and filter. 

Thankfully, maintaining proper filtration is only a two-step process. Have the filter cleaned a couple times a year (always inspecting for the conditions of the filter elements), and make sure your pump is running long enough to turn over the water at least once a day. 

(In a later blog we will take a look at running the pump and filter at the RIGHT times) 

If you are still reading this far in, then you are a pool nerd and pretty interested in pool filtration. So let’s dive into how filters work. Water starts by entering the tank through the inlet pipe creating pressure in the tank. This forces the water to pass through the filter material in order to escape the tank and return to the pool plumbing through the outlet pipe.  

Now we keep mentioning filtering material, but what does that mean? Today there are two types of filters that dominate the Southern California market: D.E. and Cartridge. There are also sand filters but they are much less common on residential pools in this area. All of these types of filters refer to the material each system uses to catch debris.

D.E. stands for Diatomaceous Earth. It is mainly made up of silica and is nearly microscopic in its individual grains. It begins its life as a white powder almost like baking soda but more fine grained. Then it is added to the system through the skimmer. The D.E. then covers cloth panels inside the filter known as grids. It is actually the D.E. that catches the debris, not the cloth panels. This makes them effective down to the extremely small particles that get trapped in these filters. However, over time the D.E. catches so many particles it can no longer accumulate any more. When this happens the filter needs to be disassembled and cleaned. The existing D.E. in the filter needs to be completely removed and replaced with fresh D.E.. It is an extremely messy process as that once white powder now resembles a gray, brown or even green mud-like substance. All of this mud should be removed from the filter tank as well.

Because of this messy process many in the pool industry have gravitated to cartridge filters. More traditional in its function, cartridges are more recognizable. They more closely resemble normal air filters and similar systems you may have seen before. By using just the material on the cartridge itself, when cleaning these filters the goal is simply to remove the accumulated debris. There is no additional ‘mud’ to wash down the drain. Simplifying the process and greatly reducing the mess. 

Both filters require bi-annual cleaning, but it is possible to have a filter that is too small for a given body of water. In that case a cleaning will be necessary more often, in some cases each month. Filters are measured and sized in the square feet of usable filter surface area. Larger filters have increased space to hold more debris than smaller filters. This allows for more time between cleaning. 

D.E. filters do filter down to a smaller molecule size. This is measured in microns, for reference a grain of table salt measures to about 100 microns. A D.E. filter has the ability to filter down to about 5 microns. Cartridges can get down to about 10 microns. This level of filtration is more than enough, sand filters only work down to about 20 while still managing to remove most of what is needed in a pool. Both D.E. and Cartridge filters provide enough filtration to keep a pool clean, but cartridges are typically less of a mess in the backyard.

If your filter needs replacing, resizing, fixing or just cleaning, our techs are trained to handle all types and would love to help you solve your filtration needs.