Pool Care and Cleaning Issues

Sanitation

Sanitation is generally accepted as the reduction of the level of microorganisms in pool water  by significant numbers. Microorganisms are living cells so small they can only be observed through a microscope. This reduction (usually 99.9% or more) to safe levels as established by state or federal authorities is necessary for health reasons.

Sanitizer is the chemical or agent that effectively kills or inactivates the microorganisms present in pool/spa water. Chlorine and bromine are the most widely used options. Other sanitizers include ozone, biguanide (PHMB), copper/silver ionization, and UV radiation.

It is important that a disinfectant be continually active in the water so that it may react instantaneously with bacteria, algae, and other organic matter as they are introduced into the water. Without this disinfectant residual, all protection for the persons using the water is lost.

Chlorine reacts chemically with a variety of materials, such as leaves, debris, dirt and twigs, to oxidize them. After full oxidation and dissipation, the chlorine that remains to prevent the growth of algae and bacteria is the chlorine residual. The chlorine residual usually refers to all the chlorine in the water.

Chlorine in the water is typically measured by a test kit in parts per million. To be continuously active and provide safe water, the chlorine residual should not be allowed to fall below 1 ppm (parts per million) and may read up to 5 ppm (parts per million) or higher without eye or body irritation.

Chlorine Chemistry

When Chlorine is defined as a sanitizer it chlorine destroys microorganisms; however, it carries out an additional function as an oxidizer. This oxidation is the “burning up” of organic contaminants introduced to the water by the bather and the environment. 

Various studies have shown that only 10% of chlorine is needed for sanitation while 90% of chlorine is used for oxidation. Debris and matter in the water can tremendously increase the amount of chlorine needed for oxidation. This is why much more chlorine is used to keep levels consistent due to high bather load or greater amounts of pollen and debris introduced into the water from nearby trees or shrubbery. This is also why it is more expensive to maintain chemicals at a pool location with a lot of tree coverage.

Microorganisms and organics both consume chlorine. This consumption is also known as the chlorine demand and is defined as the amount of chlorine that will react with contaminants before any chlorine is left un-reacted. 

Microorganisms are living creatures too small to be seen by the naked eye. Since water is an open system, they are constantly introduced into the pool by rain, wind, and the human bather. Algae, bacteria, fungi, protozoans, yeasts, and viruses are the kinds of organisms of concern. Most organisms are harmless to the human body but others are disease- and infection-causing. If not killed, these “germs” are transmitted via water to other bathers. 

Researchers have also established that non-living organic contaminants are also objectionable. 

A study at Harvard University concluded that one active adult swimmer loses two pints of perspiration per hour. Perspiration is loaded with compounds resembling the chemistry of urine. The body is also constantly shedding microscopic skin particles sloughed off by the friction of water. These are all “involuntary wastes.” Add in “voluntary wastes” such as expectorate, nasal discharge, fecal matter, and urine and you can appreciate the bather load created on the pool sanitizer and oxidizer.

Hypochlorous Acid

Reaction with Ammonia: Ammonia is one of the end products of the body’s metabolism of ingested proteins. The reaction of HOCl with ammonia produces odorous, irritating compounds called chloramines also known as combined chlorine. These chloramines irritate the eyes and mucous membranes and are often confused with pool chlorine because of their “chlorine smell.” Another negative quality of combined chlorine is that it has little ability to kill waterborne diseases.

Reaction with Sunlight: In the presence of sunlight, Hypochlorous acid is reduced to inactive chloride ion by the ultraviolet rays of the sun. On a very bright sunny day up to 90% of the active chlorine can be destroyed by sunlight within two hours. 

Types of Chlorine Residuals

1. Free Chlorine (FC): FC is the workhorse of sanitation, killing germs and oxidizing organics. At levels up to 10-20 ppm, FC has no detectable taste or smell and causes no irritation.
2. Combined Chlorine (CC): Also called chloramines, CC is formed by the reaction of FC with ammonia wastes from bathers. Combined chlorine causes the characteristic “chlorine odor” of heavily used pools and spas, and it is responsible for eye and mucous membrane irritation. Such irritation can be noticed at levels as low as 0.2 ppm. CC has little sanitizing capability.
3. Total Chlorine (TC): TC is the sum of the FC and CC residuals and is simply a mathematical expression: TC = FC + CC

Tests for Combined Chlorine 

These are the primary wet-chemistry methods for testing chlorine residuals: OT and DPD. Note that the OT method only measures total chlorine while the DPD method determines free, total, and combined chlorine residuals.

As the pH decreases chlorine’s killing ability, the presence of pathogens increases dramatically. This is why pools run at a high pH have more difficulty with algae and bacteria counts.

Breakpoint Chlorination

Once all chlorine residual levels have been determined, it may be necessary to destroy high levels of combined chlorine. This process is called breakpoint chlorination. Breakpoint chlorination is accomplished by superchlorinating otherwise known as "shocking" the pool with chlorine (typically granular). When superchlorinating, the chlorine level is increased so dramatically in such a short period of time that Superchlorination at breakpoint has the unique capability to destroy combined chlorine. 

Chemists explain that when FC (Free Chlorine) is raised to ten times the measured CC (Combined Chlorine), the level of CC will be reduced to a minimum:

Breakpoint Dosage = 10 X Combined Chlorine Level

Note: Adding less than the breakpoint dosage can create more combined chlorine!

Different chlorine sanitizers, due to their different strengths, will require different dosages to achieve the desired breakpoint dosage. This super level of chlorine also cleans the pool of oxidizable organic matter at a very quick rate and results in clean, sparkling water.

Sometimes it is necessary to lower the FC of the pool water. This could occur after a superchlorination when the pool is to be used the next morning and there is not enough time for the chlorine level to lower naturally. Here, the addition of a chlorine neutralizer, such as sodium sulfite, will instantly destroy the excess FC level.

1.       Etched plaster

2.       Corroded metals

3.       Stained plaster

4.       Eye & skin irritation

5.       Destruction of total alkalinity

1.       Scale formation

2.       Cloudy water

3.       Short filter runs

4.       Eye & skin irritation

5.       Pool chlorine efficiency

Experts generally agree the pH for swimming pool water should be between 7.2 and 7.8.

pH Value changers: Acid and some other acidic pool chemicals lower pH while Soda ash, sodium bicarbonate and various other commonly used pool chemicals raise pH. 

Total alkalinity is a leading factor in determining the speed of pH change. The ideal TA (Total Alkalinity) range is 80-120 ppm. 

pH is measured on a scale from 0-14, with a pH of 7 being neutral. Below 7, the water is acidic and above the water is basic (or alkaline). 

The pH scale is logarithmic, meaning that every whole unit increase is 10 times its predecessor.

Total Alkalinity

Total alkalinity is the measure of the ability of water to resist changes in pH . . . that is . . . the ability to “buffer” water from wide pH swings. In water that contains no buffering ability, pH can wander dramatically. This is called pH bounce—a rapid fluctuation of pH levels with the addition of small amounts of acid, base, or other pH-altering agents. This can happen after a rain storm, after a lot of debris is introduced to a pool etc etc.

The result is a highly unbalanced water condition resulting in damage to copper heat exchangers, light rings, stainless steel ladders, and concrete pool surfaces.

If the total alkalinity of your pool water is high, you add acid to lower the pH. In a matter of hours, the pH will rise. Why? Because high total alkalinity neutralizes the acid. Therefore, high total alkalinity will create an almost constant acid demand. It is, therefore, necessary to adjust total alkalinity first.

If the total alkalinity is higher than 120 ppm (plaster pools) or 140 ppm (vinyl-liner pools), acid should be added to lower it.

High temperature water has a greater tendency to scale and cold water to corrode than standard 78^o-82^oF pool water. High level of cyanuric acid can affect the total alkalinity reading.
 

Chlorine Stabilization

Cyaneric Acid was discovered in 1958. It is a weak acid often abbreviated CYA. Cyanuric acid is an odorless, white granular substance. It is also known by such names as stabilizer, isocyanuric acid, conditioner, and CYA.

It was found to reduce chlorine depletion via sunlight. In other words, cyanuric acid stabilized the free chlorine residual from sunlight destruction. When dissolved in water at 25 ppm, FC would last three to five times longer than pool water not containing CYA.

Above 50 ppm, only minimal additional stabilization benefit is achieved.

Note that cyanuric acid stabilizes Hypochlorous acid regardless of the form of chlorine used!
 

Cyanuric Acid Properties

· pH 4.5 (in a 1% solution)

· slow dissolving

· maximum solubility = 1,600 ppm

· not destroyed by any pool chemical

· removed only by draining, splash-out, carry-out, and backwash

· 1 lb./5,00 gallons yields 25 ppm CYA

Although cyanuric acid has all these benefits, it also carries with it a potentially significant downside. In the process of stabilizing FC, cyanuric acid causes the chlorine to slow down or become less effective both as an oxidizer and a sanitizer. This must be compensated for by using a higher concentration of chlorine in the pool water.

In 1958, two new products for pool water sanitation were introduced. Called chlorinated isocyanurates, or simply “isos,” they are sanitizer and stabilizer all in one.

The key to understanding the stabilized chlorines “trichlor” and “dichlor” is that their chlorine is attached to a CYA molecule. Although this one-step process has made isos very popular, operators need to be aware that CYA can build up unintentionally to an objectionable level.

This is because after the chlorine part of an iso compound has been depleted, the cyanuric acid component remains behind, dissolved in the water. CYA can accumulate faster than splash-out, carry-out, and backwashing removes it. For this reason, better test kits allow you to monitor CYA.

Trichloro-s-triazinetrione [trichloroisocyanuric acid (TCCA)

Often called “trichlor,” slow-dissolving stabilized chlorinating tablets or sticks are very popular with the homeowner as they are used in a constant feed chlorinator. Also available as granules.

ACTIVE STRENGTH

>99%

AVAILABLE CHLORINE CONTENT

90%

STABILIZER CONTENT

54%

pH

2.8-3.5 (in a 1% solution)

Sodium Dichloro-s-triazinetrione [sodium dichloroisocyanurate (NaDCCA)]

Often called “dichlor,” these white, fast-dissolving stabilized chlorinating granules are especially popular for spas and aboveground pools that need a quick dose of chlorine prior to use.

NOTE: By shocking during the day, any large dose of chlorine will be depleted at a high rate by the sun.

Calcium Hardness

Pools having too much calcium may have the calcium precipitate as scale, but pool water entirely deprived of calcium becomes "hungry" or aggressive and seeks to absorb calcium into the water from surfaces it is in contact with such as grouting or concrete.

Unless water has a sufficient hardness, it will be aggressive or corrosive and attempt to dissolve any source of calcium or magnesium around. Most often, the plaster pool will begin to dissolve because the plaster is made from calcium. In a non-plaster pool, aggressive water will start to dissolve the metallic parts of the equipment.

Too much hardness in the water causes the water to deposit or precipitate out the amount that it can no longer hold. This depositing out is called scaling. The hard white or off-white crusty material on tile, in heaters and on pool walls is scale. In addition, high hardness levels will cause the water to cloud. When water evaporates, only the pure water evaporations and it leaves behind the minerals and dissolved solids.

All of the dissolved solids, including calcium and magnesium, stay behind. In time, hardness and dissolved solids can build up. “Sufficient” hardness varies depending on pH, total alkalinity, temperature and TDS (total dissolved solids). However, it is generally agreed that the minimum level of calcium hardness is 150 ppm. The recommended range is typically 200 to 400 ppm.

Total Dissolved Solids (TDS)

The sum total of all the dissolved material in the water is called TDS. It includes hardness, alkalinity, chlorides, sodium, sulfates, salts and just about everything that has been put into the water. When water becomes filled with dissolved things, strange phenomena can occur – things like salty-tasting water, colored but clear water, algae growing despite a good chlorine reading, corrosion of metallic parts, cloudy water, eye and skin irritation, and false readings on chemical tests.

If all the water in a pool or spa were to evaporate there would be a residue left behind made up of particles too small to be caught by the filter. These solids come from the water supply, treatment chemicals added, environmental debris, and bathers.

“TDS,” which stands for total dissolved solids, is the measure of the impurities while they’re still in solution and invisible. The measurement is often an indication of how “aged” pool water is, since TDS increases over time. Although it is true water becomes slightly more corrosive as TDS increases, non-saltwater pools should have a TDS under 2,000—a reading that has little effect on water balance.

TDS buildup is inevitable. Every time chemicals are added to the water, the TDS increases. Even adding make-up water to the pull increases TDS. Evaporation is the cause. When water evaporates, only pure water evaporates, everything that was dissolved in the water stays behind. In time, this builds up.

There is no effective way to lower TDS in a swimming pool or spa except to drain all or part of the water and then refill it.

There really is no lower or minimum level for TDS – it’s just whatever you get when you fill the pool or spa, usually around 300 ppm.

Saturation Index (SI)

SI = pH + TF + logCH + logALK – CONSTANT

Where:
SL = Saturation index

pH = measured pH

TF = temperature factor

CH = measured calcium hardness

ALK = measured alkalinity minus cyanurate alkalinity

CONSTANT = combined factor for temperature and ionic strength correction, and concentration conversions.
 

When water is balanced the SI equals zero. If the SI is within ± 0.5 pH units, the water does not require attention. Variations greater than +0.5 may lead to cloudiness and scaling, while variations less than -0.5 may cause corrosion of concrete, and possibly metal surfaces.

Water Balance

Water can either corrode surfaces or deposit crusty, coarse substances called scale. Water that corrodes and/or is scale forming is called unbalanced water while water that causes no damage is balanced.

Corrosive water is “aggressive” and attempts to dissolve concrete and metals, pitting concrete and destroying steel filters and copper heat exchangers. Scaling water does the opposite—it attempts to deposit or precipitate calcium carbonate out of solution, causing unsightly deposits on pool surfaces, and possibly plugging the filter and circulation piping.

Water is known as the “Universal Solvent” – and for good reason. Given enough time, water will dissolve just about anything it comes in contact with. It will continue to dissolve things until it can hold no more – at which point we say that it is saturated. If it dissolves too much, it will precipitate out the excess. All of this is governed by the laws of chemical equilibrium, which we call water balance. The characteristics of water vary so much from area to area that we can provide no set formula.

Chlorine Enhancers

These products do not kill algae by themselves and, therefore, cannot be legally called algaecides, either in advertising or on their packaging. In addition, because they make no pesticidal claims, they do not have to be registered with the Environmental Protection Agency. The active ingredient, therefore, does not have to be stated on the label.

Chlorine enhancers work by combining with chlorine that is already in the water or chlorine that is added at the same time as the chlorine enhancer. The chlorine enhancer is, most likely, something that algae recognizes as food. When the algae ingests what it thinks is food, it gets a lethal dose of chlorine along with it.

By itself, the chlorine may not have killed the algae. And by itself, the chlorine enhancer cannot kill algae. But together, they formed a deadly combination.

Chlorine enhancers are good at killed black algae and mustard algae.

Algae

Algae are single-cell plants containing some bad stuff called chlorophyll. They are some of the hardiest and most widespread organisms living on this planet, existing in over 30,000 different varieties. There are three main categories of algae found in pool water.

Green Algae

Usually floating algae, but sometimes clings to walls. Pool water becomes cloudy with a green growth that renders the pool uninviting and dangerous to use by making it slippery and difficult to see the bottom of the pool. Before green color appears, sides of the pool feel slick, water becomes hazy, and it exhibits a high chlorine demand.
 

Mustard (Yellow) Algae

Appears as a yellow powdery deposit on the pool, usually on the shady side. Once established, it is resistant to chlorine and can exist in the presence of 3.0-5.0 ppm FC.
 

Black (Blue-Green) Algae

Black algae is usually seen in the formation of dime-to quarter size black (or blue-green) spots. These spots typically adhere to the pool’s surfaces like gum and are very difficult to remove. Black algae forms a layered structure where the first layers, which may be killed by chlorine, protect under layers from further destruction. Black algae, like mustard algae, is also chlorine-resistant.

The best algaecide (algae-killer) and algaestat (algae-preventive) is a properly maintained sanitizer level. When the sanitizer level is allowed to drop or deplete or when phosphate, an algae food, is present (usually from fertilizer runoff), algae spores (seeds) will germinate. Within 12 hours, a pool can be completely overrun with green algae. This condition is called "algae bloom".
 

Cloudy Water

Cloudy water is usually caused by a combination of these items:

1. Filtration/Circulation
2. Water Balance – With unbalanced water on the scaling side, suspended calcium carbonate is possible. By balancing pool water, the calcium carbonate particles will go back into solution and turbidity will clear up.
3. Algae Formation – An incipient algae bloom will cause the pool to cloud. This type of turbidity can be distinguished from other causes by a slippery feel on the pool’s surface. Super-shock the pool to 30 ppm FC to correct this problem. Unfiltered dead algae will also cloud water.
4. Heavy Bather Load – Heavy use by bathers at one time can overload the pool with organics, causing turbidity.
5. Fine Suspended Solids – Sometimes clay or dirt particles that are unfilterable due to their small size may become suspended in the pool water.

Bromine Chemistry

Bromine is commonly used to sanitize spas and many indoor pools. Unless the pool or spa is completely drained and refilled with fresh water it cannot be switched over from bromine to a chlorine sanitizer. Once on bromine, always on bromine. The combined bromine formed when hypobromous acid reacts with nitrogenous wastes like perspiration and urine will not irritate bathers or create strong odors. Also in contrast to chloramines, bromamines are good sanitizers.

Bromine is acidic (pH of 4.8 in a 1% solution) and may lower total alkalinity. Regular testing is a must as is treatment to replenish total alkalinity with sodium bicarbonate as necessary.

Whereas chlorine loses much of its sanitizing ability as pH increases, bromine does not.

Hypobromous acid residuals are destroyed by sunlight at a slower rate than unstabilized Hypochlorous acid, but faster than stabilized chlorine. There is no known stabilizer for bromine that even approaches the effectiveness of cyanuric acid on chlorine.

For this reason bromine pools are usually indoors.

Although there is less water in a spa than a pool, that doesn’t mean a spa is less care. Actually, a spa requires more exact water treatment, which is why it’s referred to as “teaspoon chemistry.”

Whether one adds ½ lb. or 1 lb. of chemicals to a 150,000 gallon pool is irrelevant due to the large quantity of water.  However, with the small volume of a spa, adding twice as much treatment chemical as called for could be disastrous.

Spas also have a much higher bather-to-water ratio than pools. Localized depletion of sanitizer in a 20,000 gallon pool from a group of bathers occupying only 1,500 gallons can be effectively replaced by the reserve of sanitizer in the remaining 18,500 gallons. Most spas are in the 300 to 1,000 gallon range, though, so depleting the disinfecting residual in even 200 gallons would greatly reduce the bathers’ protection.

Frequent testing is necessary to ensure spa bathers have balanced water. It is possible for only two people in a 400-gallon spa to deplete a sanitizer level of 2 ppm bromine or 1 ppm free chlorine in just 15 minutes!