by Mark Garcia November 03, 2015
What's the best pool filter type? It's a question that never stops being asked. Sand, D.E. or Cartridge filter, what's your pleasure?
Everyone has a different opinion on the best type of pool filter to use, but the fact is, all three filter types are excellent, when a proper size pool filter is used, I should say.
When buying a new pool filter, if you want to improve water quality and reduce time spent maintaining a filter, Go Big! It's going to cost you twice as much money, but will save water, energy and time. And, you won't have to worry about your pool pump being too powerful for the filter. The slower flow rate will reduce system pressure and increase filter efficiency.
Below is a pool filter comparison chart, to contrast and highlight some of the main differences between pool filter types. All 3 pool filter methods are a good choice, and all of them have legions of fans who swear by their filter of choice.
The Filter Media is what's inside of the tank, or what does the filtering. Sand filters are filled about 2/3 full with specially graded Pool Filter Sand, or filter sand alternatives. The water is pushed through the sand, which traps particles. Reversing the flow (backwashing) of water through the tank flushes out the trapped dirt and deposits. DE or Diatomaceous Earth filters use Septums or Grids, which are fabric covered plastic frames. The grids 'hold' DE powder, or the powder 'coats' the grids, and as the water passes through the grids and back out of the filter, the dirt is trapped by the diatom powder. Like sand filters, DE filters are backwashed when the dirt load reaches capacity. Cartridge filters use a pleated woven polyester fabric to trap dirt and particles. The water is forced to travel through the fabric, leaving dirt behind. Cartridge filters are not backwashed, and have no backwash valve to maintain. When the pressure gauge rises (like on all filters), 8-10 lbs above the clean, start-up pressure, it's time to remove the cartridges and hose them clean thoroughly.
All filters work a bit better when they are a bit dirty, hence the range of potential micron trapping ability in our pool filter comparison chart. A clean sand filter may filter down to only 40 microns, but as dirt loads up in the sand bed, it may effectively trap particles in the 20 micron range. All filters will maintain clear water, in a well balanced and clear pool, but only those that can trap very small particles can clean up adverse water conditions quickly. Spring pool openings or algae blooms for example; a DE filter can clean this up in 1-2 days, but sand filters can take over a week, and may need help from clarifiers or other chemicals Other factors affecting filter dirt trapping ability include the water flow rate and the filter media age. High flow rates, higher than the recommended design flow rate, will produce poor filtration, pushing smaller particles right through the filter. As filter sand or filter cartridges age, they lose up to half of their dirt-trapping power and need to be replaced - the perfect segue to our next discussion point!
The tank of your pool filter can last 25 years or more, but the filter media, the stuff inside that does the filtering, will become worn out over time, eventually becoming evident in cloudy water, short filter cycles (time between backwash or cleaning). Tired filter media needs longer filtration time, and more frequent cleaning or backwashing to keep the filter pressure low. You'll also need more sanitizer, clarifier and other chemicals to assist your ailing pool filter. Poor water chemistry can also shorten filter lifespan, and a pump that's too big can damage filter media when flow rates exceed the filter design flow rate. The size of your filter will also greatly affect the filter media lifespan. If your filter is double the size, the filter media can last twice as long - 6 years for cartridges, 10 years for sand and 15 years for DE grids.
Everyone can understand the logic of a large pool filter, but when faced with a price range of $500 - $1200, it's hard to pay double the cost for something that will do pretty much the same job. A car analogy is appropriate; a sedan and a sports car will both get you to the same place, but the sports car will get you there faster and easier (plus, you'll look better driving it!). DE filters cost the most, mainly because they have so many parts, but also remember that they do the best job, at filtering the water. Cartridge filters are cheaper than DE filters, with fewer parts, plus no separate backwash valve to buy. Sand filters are the cheapest pool filter because they are the simplest type of pool filter, with few parts and a simpler design to fabricate. All filters should have the same installation cost, however the installation of a cartridge filter is usually the lowest degree of difficulty. This is because without a filter valve, the plumbing is less complicated, and because your not hauling and pouring hundreds of pounds of filter sand, or 6-9 lbs of diatomaceous earth powder.
Sand: Pool Filter sand is very cheap if you can find it locally, usually about $10 per 50 lbs. Over time the sand will lose its sharp edges, resulting in a filter tank filled with tiny ping pong balls! Most inground pool filters use about 300 lbs of filter sand, but a larger (recommended) sand filter can hold 500 lbs, which is still a low total cost, as long as you don't pay to have it shipped! Filter sand alternatives exist however, which are cost effective to ship such as PolyBALLS, ZeoSand and Filter Glass.
DE: D.E. filter grids are the fabric coated plastic frames. Over time, the stitching will unravel or holes can develop in the fabric. If you are handy with an awl, you can sew up holes, but if they are very old or damaged from bad water chemistry, DE grid replacement is in order. Most DE filters have 8 grids, and complete DE grid sets are available for $100-$150, or individually for around $20 each.
Cartridge: Filter cartridges, like the air cleaner in your car, won't last forever. The fibers in the fabric will separate over time, and can develop holes or thin spots. It is advised to replace pool filter cartridges after 12-15 cleanings, or within a 3-5 year time frame. Large cartridge filters, with four 32" tall cartridges, can go an entire season without cleaning on some pools, and can last 6 or 7 years in some cases. Replacement costs for cartridges vary, but can be as much as $125 each for inground pool filters
Changing filter cartridges is the easiest filter media replacement; just open the tank and swap out the carts. Changing filter sand involves scooping out the sand by hand, and pouring in new sand, through the top access port. DE filter grid replacement involves opening the tank, removing and cleaning of the grids, followed by a complete dissasembly and reassembly of the filter grid assembly. Replacing filter sand or the DE filter grids are more difficult and time consuming (1-2 hrs), but certainly DIY friendly.
If you are located in a dry area with pool water use restrictions, your legislators may have already chosen your next pool filter for you! Cartridge filters are preferred in drought stricken areas because they are not backwashed; instead the cartridges are removed from the tank and hosed clean, top to bottom. This uses about 100 gallons or so, compared to 500 gallons (or so) when backwashing a sand or DE filter. DE filters however, can be 'bumped' every few weeks to reduce the need for frequent backwashing. A 'bump' is a very short backwash, just 10-15 seconds, which mixes up the dirt and DE powder, and allows you to continue filtering with delayed backwashing. DE filters can also be installed with a separation tank, to filter the backwash waste water, and return it to the pool without wasting a drop. Sand filters however, require more frequent and longer backwashing cycles, using more waste water than other filter types.
A sand filter is the simplest filter design, with fewer parts and less potential problems. It does however have a backwash valve, either multiport or push-pull valve. In fact, a sand filter will give more problems with the valve, than it will with the tank or internal parts. DE filters have the most internal (and external) filter parts - dozens of them, and also a backwash valve. And because a DE filter requires annual removal, cleaning and inspection of the grid assembly, there are more opportunities for damage or breakage (caused by you, sorry). Cartridge filters don't have backwash valves and have a very simple design, with very few parts. For this reason, it is likely that a cartridge pool filter will break less often, or require fewer repairs over time.
In the Ease of Use category, sand filters are the undisputed winners. Easy to operate and understand, easy to backwash, and you hardly ever need to go inside the tank for any reason. DE filters by contrast, require adding a fresh charge of DE powder after each backwash, and every 6 months will need to be opened up and hosed thoroughly, and inspected for missing parts or damage. Cartridge filters can be very low maintenance when they are big enough, with cleaning needed only every 3-4 months, but if small, you could be opening up the filter every few weeks. Cleaning cartridges is not hard, but have a seat, it's gonna be awhile - expect to spend at least 10 minutes per cartridge, hosing it carefully top to bottom. For best results with all filter types, use a pool filter cleaner annually, to remove minerals and oily deposits.
Thanks for Reading!