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Sand, Cartridge, or DE: Which Filter to Choose?

Satyajeet Vispute Mar 21, 2020
Unclean pool water looks and smells bad, and is a breeding ground of diseases. It is important to choose a pool-water filter to keep the pool clean. We run a comparison between three top types of pool filters. So get ready for a dip into the debate of sand vs DE vs cartridge filters for pools.

Safety Tip

One must always use an air mask while attempting to 'recharge' a diatomaceous earth filter with DE powder, as inhaling this powder can cause a feeling of sickness and spontaneous coughing.
Do you find yourself wondering whether you are swimming in a pool of water or a pool of filth every time you take a dip in your swimming pool? If you do, then you probably have the wrong filtering system installed.
The water in a swimming pool, like that in a lake, is stagnant, and thus prone to accumulation of dirt and contamination. Hence, an effective artificial filtration system is much-needed to keep the water clean.
There are basically three accepted types of filtering systems used in pools: sand filter, cartridge filter, and diatomaceous earth (DE) filter. Each of these provide a different level of filtering, and has a unique set of advantages and drawbacks when compared to the others. Choosing the right one for your pool can make all the difference.
In the following sections, we shall discuss the particulars of these filters, and highlight their pros and cons, hoping that you, the reader, by using the information provided here, will be able to decide which one is better suited to your swimming pool.

Sand Filter

If you put sand in clear water, it turns murky. However, it is sand itself which plays an important part in the natural filtration of the water in rivers. Sand filters for pools work on the same principle.

How Sand Filters Work

Sand filters comprise a compact chamber which is filled with processed sand. This sand is specially manufactured to make it suitable for the filtering process. Using machines, raw sand is ground till its particles become very small in diameter. They also become very rough and coarse.
It is because of their coarseness and small size that these particles are able to trap dirt particles, which range from 20 microns to 40 microns in size. Some modern-day sand filters use sand with particles which are so small, that they can even catch dirt particles which are as small as 12 microns.
The swimming pool's water pump outlet is connected to the inlet of the sand filter system. The unclean water being pumped in, passes through the sand packed inside the filter's chamber, which traps and removes dirt particles and debris from it.
The clean, filtered water then flows out of the outlet of the filter, through the connecting pipe and finally into the pool.Periodically, the accumulation of dirt and debris clogs up the system, and then the filter system performs a 'back-wash' to wash away the clogs and clean the sand within it.
This process is activated by putting the flow control knob in the 'back-washing' position, which redirects the water in the filter so that it flows out of the back-wash hose, and away from the pool rather than in it.

Advantages of Sand Filters

1. Sand filters can remove dirt particles which are 20 - 40 microns in size, with some modern ones even capable of extracting particles as small as 12 microns.
2. They are easy to use and operate. Routine maintenance too is easy, and the sand requires refilling only once every 3 - 5 years.

3. They are ideal for pools having pumps with a large gallons-per-minute count.

4. These are an efficient and cheap solution for most pools.

Disadvantages of Sand Filters

1. Very fine particles can pass through the sand in the filter and might enter the pool.

2. The sand in it requires frequent cleaning, else clogging of the filter takes place.

3. As the degree of blockage in the filter increases, the back pressure on the water pump increases as well. This decreases, both, the pump's energy efficiency and working-life.

Cartridge Filter

A cartridge filter utilizes a paper or polyester filtering element, which is designed such that it allows free flow of water, but restricts the passage of impurities within it. Typically, it can remove twice as much dirt from the water as a sand filter can.

How Cartridge Filters Work

This filter system includes a large tank. The tank houses the filter element in the form of a cartridge, which covers its entire volume from top to bottom.
Water pumped by the swimming pool's water pump enters through the filter's inlet into this tank. There, as it passes through the filter cartridge, impurities in the water get stuck to the filter, and clean, filtered water escapes out of it, and finally travels to the swimming pool via the outlet hose.
The use of a paper/polyester filter element allows for much finer filtering. These filters are capable of trapping particles as small as 8 microns. Thus, all the minute dirt particles, and in fact even oils get stuck to the filter cartridge, ensuring that the water at the outlet is clean.
The large surface of the tank ensures that the filter doesn't get clogged up easily. This relieves back-pressure, and allows it to be used in conjunction with water pumps having lower gallons-per-minute rate.
The maintenance of cartridge filters is largely depended on the level of contamination of the pool water. However, cleaning the filer cartridge is as simple as removing it from the tank and rinsing it with water, preferably with a detergent. A single cartridge can last up to 3 years on moderate usage and regular cleaning.

Advantages of Cartridge Filters

1. Its larger filtering area traps more dirt particles and greatly reduces the chances of clogging.

2. This system is able to trap particles as small as 8 - 12 microns in size. Thus, it outputs much cleaner water.
3. It requires less frequent cleaning, as the large surface area doesn't clog easily.

4. The chances of back-pressure on the pump too are low, which increases the water pump's energy efficiency and working life.

Disadvantage of Cartridge Filters

1. The initial cost of a cartridge filter is higher than that of a sand filter.

2. Since it traps a larger number of particles, it can quickly become dirty if the pool is frequently used. In such cases, even after regular maintenance, the cartridge may reach the limit of its working life much sooner than expected, and subsequently would need to be replaced.

Diatomaceous Earth (DE) Filter

The name diatomaceous comes from the fact that these filters comprise a filtering media which is made from the crushed fossilized exoskeletons of diatoms. These exoskeletons are porous, and allow only water to pass while filtering out the dirt and debris from it.

How DE Filters Work

At the final stage of installation, the filter system requires you to feed diatomaceous earth powder to it via its in-built skimmer. When the pump is on, this powder flows with the water till it reaches a cloth membrane, called the 'septum', where it is collected.
As you keep adding more powder, its deposition on the septum continues till a layer is formed on it. Typically, powder is added till this layer is about half an inch thick. The particles of the powder compress under the water's pressure and the layer so formed adheres to the septum even after the pump is turned off. Thus, the filter becomes ready for use.
Water to be filtered passes into the inlet and is filtered by the layer of diatomaceous earth powder. It is capable of extracting dirt particles which are as small as 3 microns, and thus, the output water is literally good enough to drink.
After initial installation, this filter system will continue to work reliably for up to a year without requiring any maintenance. During that period, back-washing may be required, but only once or twice. After a year, the filter may require refilling of the DE powder. This can be easily done by purchasing and adding more DE powder to the system.

Advantages of DE Filters

1. This filter can trap particles which are as small as 3 microns in size. This means that the water at the output is literally at its purest. This helps the pool achieve an unparalleled level of clarity and cleanliness.
2. The greater level of filtration removes almost all the organic debris from the water. This significantly reduces the number of bacteria in it.

3. This filter has a very long interval between recharge. Thus, maintenance requirements are pretty low.

Disadvantages of DE Filters

1. Back-washing and recharging the filter requires time and effort. You also need to follow a step-by-step procedure to accomplish it.
2. Sometimes, diatomaceous earth adheres to the septum so strongly that the normal removal procedure doesn't remove it completely. In such cases, one might be required to disassemble the delicate assembly of the filter, and manually clean the filter.
Thus, each of these three filters have a distinct set of advantages and disadvantages. For medium levels of filtration, the sand or the cartridge filters should suffice. However, if you really desire sparkling clean water in your pool, then the diatomaceous earth filter should be your choice.