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    Pool Filter Selection: Sand or DE or Cartridge?

    August 29, 2014
    chrislow

    filter-media-types

    When it comes to filtering your swimming pool water there are 3 different types of pool filters that are used - Sand, Diatomaceous Earth (DE) and Cartridge Filters.  Everyone has a different opinion on which filter is the best and which one will give you the least amount of maintenance. I will explain the pros and cons of each inground pool filter type so you have enough information to make an educated decision on which pool filter is best for you and your swimming pool.

    All pool filters remove dirt through a screening process which I will explain for each one.Swimming pool filters are rated, or sized in 2 ways, filter area and filter rate. The filter area is the total area or square feet of filter media of surface of which water can flow through. Filter rate is measured in gallons per minute, per square foot of filter area.

    sand-filter-cutaway-3Sand Filters - The oldest form of filtration for a swimming pool, sand filters work by filtering water through a layer of #20 US grade silica sand. The dirt particles in the water are trapped and held in the very small openings between the fine grains of sand. With a sand filter water enters the filter through the top of the filter and then is evenly distributed across the surface area of the sand bed, and pushed to the bottom of the filter.

    A new sand filter or a sand filter with new clean sand will begin to work better and filter to a smaller particle size as the sand bed loads with small debris. As the filter gets dirtier the flow of water through the filter will decrease because of the increase in pressure across the sand bed. As the flow rate decreases, the pressure rate increases.  When the pressure rate increases 7 or 8 psi above the starting pressure, the filter needs to be cleaned, or backwashed. Backwashing causes the water to flow in reverse, upward through the sand bed and out to waste.

    Sand filters are probably the most common type of filter used and also typically the least expensive type of filter to purchase. On the downside, they are the least in terms of filtering ability, they filter down to a particle size of 20-40 microns. Besides backwashing the filter there is very little maintenance that is required you just need to change the sand about every 7 years.

    de-filter-cutaway-4DE Filters – Diatomaceous Earth is a much different type of filter media used to filter swimming pool water. Unlike a sand filter in which the sand media in the filter is cleaned and reused the DE powder is discarded along with the dirt when the filter cycle is completed and you backwash the filter. Every time you backwash a DE filter you need to add more DE powder through your skimmer. There are 2 different types of DE filters the vertical grid filter and the regenerative filters also known as bump filters. In both cases, the DE powder coats the elements inside, and traps the dirt as the water flows through the powder.

    DE filters have the advantage of filtering the pool water to smallest microns and will keep the water cleaner than a sand filter or a cartridge filter. The disadvantage of this type of filter is that it requires the most amount of maintenance. DE powder is needed after backwashing. Some states require a separation tank when using a DE filter to keep DE powder from streams or sewers. Also with a DE Filter you typically have to take apart the filter once or twice per year, to clean the filter grids or tubes with water. Typically a good hosing is all that's needed.

    This filter definitely requires the most of maintenance but it will filter the water to the smallest micron size, around 2-3 microns.  Although DE filters are the most expensive to purchase, and they require more maintenance than other types, they are the best form of filtration available. 

    cartridge-filter-cutaway-3Cartridge Filters – Cartridge filters use a pleated polyester cartridge to filter the water. One advantage of this type of filter is that there is no multiport valve necessary so the plumbing of the filter is a little easier. Since there is no multiport valve with a cartridge filter there is obviously no backwashing which will save water and money as you are not constantly backwashing chemicals out of the swimming pool. This type of pool filter is considered the most environmentally friendly because it conserves water, and no chemicals or DE are being discharged on to the ground.

    The cartridge filter will filter the water to almost as small as microns as DE filter and with less maintenance because it is removed and manually hosed clean with a garden hose. A big disadvantage of a undersized cartridge filter is that you'd need to clean the cartridge fairly often, but a larger filter, with a cluster of 3 or 4 cartridges inside, you normally only have to clean the filter every 4-6 months.

    To clean the cartridges you open up the filter tank and take cartridges out and spray them down with a hose, or you can use a filter cleaner to soak overnight and then spray clean the cartridges. Cleaning the cartridges is a lot easier than cleaning DE filter grids, I just pull up a chair, and spray each cartridge for 2-3 minutes.  

    There are advantages and disadvantages to each type of inground pool filter and everyone has a different opinion of which is better within the pool industry. They're all good, as long as it's not too small.

    When it comes to a cartridge filter bigger is always better for less maintenance but when it comes to the DE and sand filters you must size the filter according to your pool pump, so the water flow rate meets design rate of flow. But again, for DE and Sand, bigger is also usually better.

    Pool filter selection is just another of those discussions we have with our DIY pool kit customers. Our inground vinyl pool kits include a Hayward 24 inch sand filter, a perfect fit for most folks, but there are pool filter upgrades available. For example, you could increase the sand filter to a 27" or 31" tank size, or opt for a 325 or 425 sq ft cartridge filter.

    A larger filter will give you longer filter runs, with less overall maintenance required. It also makes fast work of cleaning up poor water conditions or helps prevent them in the first place. So, the question is not really "what type of filter should you buy", but "what's the largest filter your budget can buy?".

    Talk to you later;  

    Chris Low
    SPP Pool Expert  

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    chrislow
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