One of the advantages of above ground pools is that the pumps and filters are sold as one unit. These pump/filter systems are usually attached to a single base and are much more economical than an individual pump and filter. Here we'll cover the basics of both pumps and filters for above ground pools.
The necessary size (or horsepower) of the pump can be determined by the following general rule - for above ground pools up to 24 ft round, use a 1 HP pump and for above ground pools over 24 ft round, use a 1.5 HP pump. That was easy, wasn't it? Many pool owners tend to think, "the more horsepower the better". Actually what’s best is to get the proper horsepower for your pool. Too much power and the water will be pushed through the filter too quickly for proper sanitization. Also, you will use more energy to run at a higher horsepower. Most manufacturers do not go higher than 1.5 HP for above ground pool pumps because it's unnecessary.
For above ground pool pump and filter systems, the manufacturer will pair the proper horse power pump with the proper size filter. So all you really need to do is measure your pool and follow the rule above. That will guide you to the correct size pump. Now if you are replacing an existing pump and not the filter, you will need to make sure you get a pump designed for above ground pools. Above ground pool pumps are usually postioned below the water line (i.e. on the ground next to your pool). Because they have to force water upward, pumps for above ground pools are designed differently than those used for in-ground pools (where the pump is typically above the water line of the pool). When replacing a pump for an above ground pool, just make sure you purchase one that is categorized as an "above ground" pump. Most of the time, you will see pumps divided into two categories, above ground and in-ground.
Most above ground pools currently in use have single speed pumps which run at one speed at all times. In response to growing energy costs and environmental concerns, manufacturers have begun making dual speed pool pumps which have low and high speed settings. These two settings allow you to run the pump at a lower speed for basic pool circulation and then switch to the higher speed when additional power is needed for water features, backwashing a filter, vacuuming the pool or any other application that requires more power. Dual speed pumps offer significant energy savings and are now required by law in some areas, the entire state of California being one of them. Another advantage is that the low speed setting of a dual speed pump operates more quietly than a single speed pump.
If you are purchasing a pump and filter system and you've already determined the correct pump horse power based on pool size, your next decision will be the filter. You'll have a choice of three filter types: sand, cartridge and D.E. We'll outline the benefits and disadvantages of each.
The oldest and most common method of above ground pool filtration is sand. Sand filters use special filter sand, normally .45 to .55 mm (also known as pool-grade 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 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 filters definitely provide adequate filtration for above ground pools but the other two types offer better sanitization. For maintenance, sand filters must be backwashed periodically.
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. 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 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 filters will trap particles 10 to 20 microns in size. 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 filter cartridges. If cleaned regularly, the cartridges should last one to two pool seasons depending on pool usage.
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 (see photo). 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 filters, when a D.E. filter becomes dirty, it is cleaned either by backwashing the clogged D.E. to the “waste” line or regenerating and draining. 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 filter is the maintenance.
We recommend thoroughly cleaning the D.E. grid elements (pictured at left) 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. 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. As an above ground pool owner, you will have to decide if you want to spend more time or more money on filtration.