Achieving Ultimate Water Clarity

Operating a sustainable aquatic facility is exceptionally important these days. Managers are seeking new methods to achieve the ultimate in water quality, combined with energy-efficient technology. While a marriage of the two is ideal, the priority is to strive for clean, clear healthy water all day, every day.

Water clarity can be verified in several ways. Most health departments suggest that pool clarity is determined if the main drain can be clearly seen from the pool deck. An effective technique is to toss a Secchi disk into the pool and determine if the 2-inch disk can be seen at the bottom--the black and red quadrants on the disk should be clearly visible through 15 feet of water. In actuality, though, water clarity can be measured as turbidity--the higher the turbidity, the more cloudy the water. Current quantitative indicators for measuring turbidity are the Nephelometer or Turbidimeter. NSF International recommends that pool-water turbidity should not exceed 0.5 NTUs. Most state codes do not allow turbidity to exceed 0.5 NTUs.

Filtration is critical to attaining ultimate water clarity. Traditional filtration media are still accepted by local and state health departments; however, aquatic operators are seeking greater clarity, with less effort using systems that are also easier on the environment. I will review alternative filtration technologies and how they operate so operators and managers can determine which system is best for their pool.

Sand Filtration

Sand filtration is the oldest type of pool filtration. Traditional sand filtration--whether it is a high-rate or rapid-rate filter--requires a medium that will gather the smallest particulate matter. The filters are designed to accept a granular medium. High-rate systems require fine high-grade silica sand, while a rapid-rate system uses a combination of sand and gravel. According to the NSPF Pool & Spa Operator Handbook, rapid-rate sand filtration will remove particles at a size of 50 microns, and high-rate sand will remove particles to 25 microns. Technological advancements to achieve smaller micron removal are now widely accepted in public-pool applications; zeolite and crushed glass are becoming acceptable sand-filtration media.

Zeolite is a granular volcanic material that is extremely porous. Manufacturers of these filtration products indicate that these media can remove particles down to 0.3-0.5 microns. Since the active ingredient is Clinoptilolite, it has a greater surface area with large pore spaces, allowing more dirt to be absorbed into the media. One of the greatest features of these products is the ability to remove chloramines and ammonia from the pool water.

Chloramines irritate bathers’ eyes and create odors (chlorine smell), found in indoor-pool environments. They are among a number of risks patrons and employees may face, particularly at indoor facilities. Most of the zeolite products require fewer materials, i.e., 50 pounds traditional sand; zeolite requires only 25 pounds. Mined naturally from volcanic rock, it is environmentally friendly. Because it is filtering smaller particles and is more efficient, the operator does not have to backwash as frequently, thus saving on water-replacement costs and time. Pool operators should be aware of specific guidelines, and follow directions when initially changing over to this product.

Recycled Crushed-Glass Sand Media

Larger aquatic facilities are using recycled crushed-glass sand media as an alternative to silica sand. Under a microscope, the crushed glass has angular properties that trap dirt at a higher rate. A 1998 study prepared for Clean Washington Center, a division of the Pacific Northwest Economic Region, showed that turbidity is reduced by 25 percent. In addition, there was increased backwash efficiency, with a 23-percent reduction in water used for backwashing; also, 20 percent less glass than traditional sand was required for filtration. The study indicated that using crushed glass in high-rate sand filtration reduced turbid particles in a shorter time. Glass was found to be 20 percent less dense than silica sand, thus less of the product is necessary to achieve water clarity. As a comparison, 42 pounds of crushed glass would be added instead of 50 pounds of sand. The study reported that the time to complete the backwash was lowered from 3:31 minutes to 2:34 minutes. The crushed glass has a lower density, and is lighter in weight. As with the zeolite, there is increased backwash efficiency, thus reducing the replacement water costs and the time to perform the job.

Cartridge Filtration With Antimicrobial Protection

Great advancements have been made in cartridge filtration; not only are larger cartridge filters being manufactured, but the fibrous materials are more effective in achieving improved water clarity, as well as eliminating some bacteria. Traditional cartridge filtration will trap particles down to 15 microns. This ability to trap smaller dirt particles enhances water clarity.

Some cartridge fibers now are impregnated with additional minerals to effectively eliminate bacteria growth. The antimicrobial protection inhibits the development of bacteria, thereby reducing stains and odors. Some of these cartridges are imbedded with silver zeolite, and are colored green. Operators should understand that these antimicrobials are not a replacement for proper water chemistry and disinfection. The protection is limited to the cartridge surface only.

Diatomaceous Earth (D.E.) Regenerative Filtration

For decades, diatomaceous earth filtration systems have been proven to provide the best water clarity. The benefit of using D.E. filtration is the reduction in turbidity down to 4 microns. Some of these systems are pressure systems (the water goes from the pool, through the pump and through the filter) or vacuum systems (the pump pulls the pool water through the filter elements). Either process delivers excellent water clarity. However, one negative is the time it takes to clean the filter elements. Newer technologies now allow easier cleaning through the regenerative filtration method. The benefits of using this method include the ability to remove even smaller particulate matter as well as environmental advantages such as water conservation and reduction in chemical costs.

Regenerative media utilize either traditional diatomaceous earth (skeleton-like fossils of diatoms) or synthetic fibers from wood pulp. The mechanical operation of the system remains the same regardless of which materials are used.

The key to removing particulate matter is the square footage of the filter’s surface area. The basic mechanics of regenerative media filtration are similar to those called a “bump filter,” which allows for more filter surface area. Bump filters are designed with a series of long, tubular elements made of fiber, which “dangle” from a manifold. These flexible tubes provide support to hold the medium in place. The D.E or synthetic powder adheres to the tubes and traps the dirt and debris particles. The system’s processes are mechanized to pressurize and then depressurize, causing the filter element to move in an upward and then downward fashion. Regeneration redistributes the medium, thus extending the life of the medium. The final phase is to vacuum the soiled medium and regenerate with new filter powder. Water savings is a major advantage with this system as there is no backwashing required, thus no make-up water. This saves not only water and time, but costly chemicals from being flushed down the drain. And, it reduces the potential environmental impact of flushed chemicals. Heated pools reap an added benefit--the pool heating systems are not expending energy to reheat the pool due to the addition of cooler make-up water.

Recent scientific studies have shown that there is an additional health benefit with the use of these systems: the elimination of Cryptosporidium (Crypto). The utilization of D.E. or synthetic fibers has been found to provide a second layer of protection against recreation water illnesses, including Crypto. Of course, regenerative media are not a replacement for chemical sanitation processes.

As aquatic facilities research sustainable energy strategies to achieve a greener environment, filtration methods should be addressed. Whether the operator wants to replace the sand for an alternative medium to achieve water clarity; or change out the system to cartridge or regenerative D.E., the key is reducing environmental impact and improving overall savings. However, these media may present budget concerns. At the end of the day, by making the shift, management will experience better water clarity, reduced water usage (thus lower water bills) and increased bather comfort, while delivering the ultimate: a healthier body of water for patrons and a greener facility for the future.

Works Cited:

CWC Study (

Dr. Amburgey, Filtration research (

World Aquatic Health Conference Seminar 2008: Cryptosporidium Oocyst Properties and Control with Swim Diapers and Filters

World Aquatic Health Conference Seminar 2009: Latest Developments in Crypto Removal by Swimming Pool Filters

NSPF Pool & Spa Operator Handbook (

Connie Sue Centrella is a professor and Program Director for the online Aquatic Engineering Program at Keiser University eCampus. She is a four-time recipient of the Evelyn C. Keiser Teaching Excellence Award “Instructor of Distinction.” Centrella is an industry veteran with over 40 years experience in the pool and spa industry. She is a former pool builder with extensive knowledge in pool construction and equipment installation as well as manufacturing.