Pool Filters
Swimming Pool filters are defined by the medium inside the filter tank that provides filtration and there are three types - sand, cartridge and D.E. (diatomaceous earth). Each one has its benefits and drawbacks which we'll discuss below.
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Sand Pool Filters
The oldest and most common method of filtration is sand. Sand pool filters use special filter sand, normally .45 to .55 mm (also known as pool-grade #20 silica sand), which you can usually find at home improvement stores like Home Depot. This sand has sharp edges that serve to separate particles, allowing filtration to take place. Sand pool filters are the least expensive of the three filter types which make them very popular however they only filter particles 20 to 40 microns in size. This means that particles smaller than 20 microns are not filtered by sand. Sand pool filters definitely provide adequate filtration but the other two types offer better sanitization. For maintenance, sand filters must be backwashed periodically which we'll cover in more detail below.
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Cartridge Pool Filters
Cartridge filtration has been available for a relatively long time, and recently has begun to enjoy rapid growth and acceptance. This type of filter holds one or multiple cartridges inside the filter tank. These cartridges are pleated, with a paper-like look and feel. The actual material is usually comprised of polyester fibers. The pleats increase the filtration surface area and you will see cartridge filters rated by square footage. This refers to the total area provided by all of the pleats in the cartridge. When water passes through a cartridge pool filter, debris catches on the surface of the cartridge element. When clean, the cartridge will trap larger particles, with finer particles being filtered out as the pores become clogged by the larger debris. Cartridge pool filters will trap particles 10 to 20 microns in size.
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The cartridge element can be removed and cleaned by pressure washing inside and out with a garden hose. This easy maintenance is the most popular feature of cartridge filters. The disadvantage is that the replacement of cartridges is more expensive than sand or D.E. Generic versions of the original manufacturers' cartridges are available for many models and will save you some money.
As the cartridge collects particles from the water passing through, the build-up of debris and dirt will cause the flow of water to decrease. In turn, the gauge pressure will rise. When the pressure rises 7-10 psi above the starting pressure, or when flow decreases below desired rate, it is time to clean or replace the pool filter cartridges. If cleaned regularly, the cartridges should last one to two pool seasons depending on pool usage.
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D.E. Pool Filters
Many pool professionals consider filtration by diatomaceous earth (also known as D.E.) to be the finest because it is capable of removing smaller particles than either sand or cartridge. D.E. is a powder comprised of the fossilized remains of diatoms, a type of hard-shelled algae. The individual grains of powder have microscopic openings which look like tiny sponges when magnified. Water can pass through these openings but particles as small as 1 to 3 microns are trapped during the first pass through the media. All D.E. filters have internal elements called grids that are coated with D.E. powder. It is this “filter cake” that strains dirt, dust, algae and some forms of bacteria from the water. Like sand pool filters, when a D.E. pool filter becomes dirty, it is cleaned either by backwashing the clogged D.E. to the “waste” line or regenerating and draining.
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To restore filtration, a fresh “charge” of D.E. is added to the filter. D.E. powder is fairly inexpensive so the main drawback to this type of pool filter is the maintenance.
We recommend thoroughly cleaning the D.E. grid elements at least once a year. Remove the grids according to the instructions in your owner's manual and hose them off with a forceful stream of water from a garden hose. Fill a large plastic container with warm water and add about a 1/2 cup of automatic dishwasher detergent. Soak the grids in this solution for about 3 - 4 hours. After soaking, rinse off the elements again before replacing them inside the filter.
To wrap it up, sand filters are the most economical option but require periodic backwashing. Cartridge and D.E. pool filters are more expensive than sand but offer better filtration. Of these two, the cartridge will be the easiest to maintain but more costly when it comes to replacing the cartridges.
Backwashing
Over time, the dirt and debris that collect inside the filter will cause the flow of water to decrease. When this happens, it is time to backwash your filter. Backwashing reverses the water flow through the filter and directs it to the bottom of the tank, up through the sand. This will flush accumulated dirt and debris out through the waste line. The general recommendation is to backwash your filter when the pressure reaches 10 psi over the initial start-up pressure. For example, if the start-up pressure is 15psi, you should backwash when the pressure reaches 25psi. The owner's manual for your particular filter should contain backwashing instructions. Basic guidelines for backwashing a sand pool filter are as follows:
- Turn off your pool pump.
- Set the multiport valve on your filter to the backwash position and open your backwash gate valve.
- Turn on your pump and run it for 2 minutes, then turn it off.
- Set the multiport valve to the rinse position.
- Turn on the pump on and run it for 1 minute, then turn it off.
- Set the multiport valve to the backwash position.
- Turn on your pump and run it for 2 minutes, then turn it off.
- Set the multiport valve to rinse position.
- Turn on your pump and run it for 1 minute, then turn it off.
- Set the multiport valve to filter position.
- Close filter backwash gate valve and turn pump on.
- Check the pool water level after backwashing and add more water if necessary.
For backwashing a D.E. pool filter that has a multiport valve, it is similar to the basic guidelines above; you can refer to the owner's manual for instructions for your specific filter model.
The Hayward Perflex D.E. filters have a bump handle on the top of the tank which is a convenient self-cleaning mechanism. The backwash instructions for the Perflex are a little different from those above:
- Turn off your pool pump.
- Open the filter backwash valve.
- Use the bump handle slowly 15 times.
- Turn on your pump and run it for 2 minutes, then turn it off.
- Use the pump handle slowly another 15 times.
- Turn on your pool pump and run it for 1 minute, then turn it off.
- Close the filter backwash valve.
- Turn your pump back on.
- Add D.E. to the pool skimmer located closest to pool pump.
- For Hayward EC-40 / EC-50 filters, use 3 lbs of D.E.
- For Hayward EC-65 / EC-75 filters, use 5 lbs of D.E.
- Add D.E. to the pool skimmer slowly to avoid clogging it.
- Check the pool water level after backwashing and add more water if necessary.
Filter Valves
Valves control the flow of water to the pool filter. Pool Filter tanks are designed either with ports on the top or the side where the valve will attach. There is no difference in performance between top-mount and side-mount valves. The main reason you would chose one over another is a matter of plumbing and which style will best fit your particular installation. For instance, if the filter is to be installed in a location without much space above it, a side-mount valve might be easier to access.
Sizing a Pool Filter
Filters are rated by the manufacturer with a “flow rate” which is how many gallons per minutes they're designed to handle. The larger the filter, the higher this flow rate will be. If your in-ground pool is new and you are purchasing a pump and filter for the first time, you will want to start by calculating how many gallons of water are in your pool (see our Pool Volume Calculator). Once you have this number, it is fairly easy to figure out what you will need to circulate and filter the water in your pool.
As an example, let's say you have a pool volume of 20,000 gallons. Ideally, you want to filter or “turn over” all of that water within an eight hour time period. So you divide 20,000 gallons by 8 hours and get a gallon per hour rate of 2500. Since filter and pumps are rated by gallons per minute (gpm), you would then divide 2500 by 60 which gives you a gallon per minute rate of about 42. This means you need a pump with enough force to circulate the water at a rate of 42 gpm, and your filter's flow rate has to match this. We recommend over-sizing the filter to be absolutely certain it can handle the flow coming from the pump. So in this case, instead of getting a filter rated at exactly 42 gpm, you should select one that is a little higher – around 60 gpm would be fine.
If your pool filter is too small for the pump, there will be additional strain on the pump motor as it tries to push water through and meets resistance at the filter. This will eventually burn out the pump motor and your filtration will also be compromised. Another benefit to over-sizing the pool filter is that a larger filtration area means a longer time between cleanings. It is always better to go with a slightly larger filter than you need.
If you are replacing just the filter but keeping your existing pump, you have two options. If your current filter is properly matched to the pool pump, you can purchase the same model. All you would need is the make and model number from the filter. Sometimes, a particular model has been discontinued by the manufacturer. In this case, it is usually easy to find a comparable model based on the information from your current filter.
Your other option is to figure out how many gallons per minute your pump is circulating and then select a filter based on that. The easiest way to do this is to get the make and model number from your owners' manual or the label on the pump itself. Keep in mind that pump motors often have a label that displays the model number of the motor only. Since pump motors are all made by third-party manufacturers, this number will usually not pertain to the complete pump. Ideally, you want the information for the complete pump such as “Hayward Super Pump, model SP2605X7”. Once you have this information, the most manufacturers should be able to provide you with the gpm rate for the pump. You would then select a filter with an adequate flow rate to match the pump.
For above ground pools, the pump and filter are usually packaged together on one base. This makes sizing the filter much easier than it is for in-ground pools. Since the filter is already matched to the pump by the manufacturer, you only need to be concerned with the horse power of the pump. The guideline for above ground pools is to use a 1 horse power pump for pools up to 24 feet round and a 1-1/2 horse power pump for pools over 24 feet round.
Installing a Pool Filter
These are basic guidelines for filter installation intended to give you an idea of what is involved. We recommend professional installation but if you decide to install it yourself, you must closely adhere to the specific instructions outlined in your owner's manual. A pool filter system should be installed on a level concrete slab, very firm ground or equivalent, no more than six feet above the pool water level. Be sure to position the filter so that the plumbing connections, control valve and winter drain are easily accessible for operation, service and winterizing. Once properly positioned, fill with proper medium (sand, cartridge or D.E.) according to manufacturer's instructions. Following the directions in the owner's manual, assemble the pool filter control valve and connect to the filter. Then connect pump to the control valve opening marked “pump” and the return line to the valve opening marked “return”. Complete any other necessary plumbing connections, suction lines to pump, waste, etc. Make electrical connections to the pump per instructions in the pump owner's manual.
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