With the recent freeze, several Dallas area pool owners have had the unfortunate circumstance of having to replace their filters due to cracked filter bodies. In many cases it’s not economically feasible to repair the filter which leaves the customer with the choice of which type of filter to go back with.
In order to intelligently discuss what type is better, you need to have a little understanding about how each filter type works. The purpose of the filter is to filter out solid matter (leaves, dirt, sunscreen oils, algae, etc.) Basically anything big enough to be caught in the filter and this is the basic measure of how well the filter works. In order from most effective to least effective filtration, the DE filter is best, followed by the cartridge, followed by sand which is least effective.
The DE filter works with a system of internal grids upon which the Diatomaceous Earth settles on and basically most anything that passes through the DE gets stuck to it. When you backwash the filter, the dirty DE along with everything attached to it gets flushed from the system and you start again with new DE.
A cartridge filter uses a pleated paper element or series of elements to capture dirt. When the filter needs to be cleaned, you disassemble the filter body, and remove the filter elements to clean them, then return them, reassemble the filter and start over. There is no additional medium like DE. The structure of the filter element is what traps the solids.
A sand filter uses a (semi) permanent sand bed to capture dirt. Easiest way to picture a sand filter is water coming in the top and as it runs through to the bottom to be pumped back to the pool the particles of sand ‘catch’ debris and it sits towards the top of the sand bed. When you backwash your sand filter, you’re basically reversing this process pushing debris off the top of the sand bed down the drain. You rinse the bed and start over again with relatively clean sand.
The big difference between the 3 types of filters is how small the particles are that the filter can catch. According to Hayward’s Research a sand filter can catch debris that is 20-40 microns. A cartridge filter catches between 10-15 microns. And a DE filter can catch debris as small as 2-5 microns.
The problem with DE filters is reliability and ongoing maintenance. A perfectly functioning DE filter may catch particles down to the 5 micron size, but a filter with a eraser size hole in one of the grids won’t even be able to catch the DE and now you’ve got a mess of DE in the pool in addition to repairs. DE filter service is a routine maintenance issue. It’s not a big deal to replace a grid, but owners have to expect that its going to happen.
A cartridge filter seems less appealing because of the larger micron size, but the reality is that most anything in the water that is visible is much greater than 10 microns in size. In pools that have an algae bloom for instance, the dead algae can still often be filtereed out by a cartirdge filter, whereas a DE filter might clog up after just a half day, and a sand filter might need to be run for days to clear as only a portion is caught in the sand bed.
Because of the additional reliabilty inherent in cartridge filters, while maintaining a good rate of micron filtration, my recommendation is to generally go with cartridge filters in either new construction or retrofit. The cost is about the same either way and the long term costs favor the cartridge systems. If you’re in the Dallas or Richardson area and would like to discuss replacement costs, give North Texas Pool Service, Inc. a call at 214-989-3888. We generally don’t recommend sand filters in residential applications.
If you have any questions or comments or disagree, I’d love to hear from you. You can either comment here or contact us at the office or via email.