colloidal silver, or silver particles suspended in a liquid. Silver algicides are often recommended for fighting against black algae. They are not recommended as preventatives but rather as curatives, because sunlight causes the formation of silver oxide, which is black and stains surfaces. Also, silver algicides are expensive and difficult to find.

Sequestering Agents

Metals get into pool and spa water from a variety of sources, but all common water supplies also contain metals because water naturally removes minerals from rocks and sediment. Those minerals are soluble in water.

Metals are also added intentionally to pool water as algicides. Pools equipped with ionizers or mineral systems also contain a higher concentration of copper, silver, and sometimes zinc.

The problem with high metal content in pool and spa water is that it stains surfaces and can change the water color. For this reason, the level of metals in water should be kept as low as possible.

Sometimes, it is possible to determine the type of metal present from the stain produced.

High copper levels produce a light blue or green color to the water. It can result in turquoise or black stains. It is commonly confused with algae. It is copper, not chlorine, that turns blond hair green.

Manganese can produce a blackbrown- purple color. Extra chlorine or high pH can cause it to come out of solution.

Iron is very common in source water, especially river or well water. Dissolved iron can be oxidized by chlorine and can turn the water a yellowish color. Chlorine will also produce a rusty brown precipitate that can stain the surfaces brown or tan.

If the pool water has a high metal or mineral concentration, sequestering agents should be added to the water to control scale or metal staining on pool wall surfaces. They are best used as preventative maintenance against stains, but they can be effective at diminishing existing stains.

Sequestering agents work by trapping metals that are dissolved in the water. It is an ionic interaction, where the negative sequestering agent is attracted to the positive metal ion. Sequestering agents are also called chelating agents because they grab the metal like a claw. In fact, the word is derived from the Greek word for claw. The effect is to prevent the metal from forming an oxide.

It’s important to remember that sequestering agents do not destroy or remove metals from the pool water. Rather, they encapsulate the metal. Most of the time, that complex is still too small to be filtered out of the pool. Furthermore, oxidation reactions will occur that break down the sequestering agent, leaving the pool susceptible to future staining. If the water has a high metal content, it will need repeated doses of the sequestering agent.

Regardless of their brand name, most chelating chemicals come in three categories.

The most common is made from a molecule called EDTA, or Ethylenediaminetetraacetic acid. EDTA binds iron, calcium, and other metal ions through six atoms. It is an organic compound that contains carbon, hydrogen, nitrogen, and oxygen. Like many sequestering agents, chlorine and other oxidants will cause it to break down over time. It is also susceptible to ultraviolet degradation. Nonetheless, many service professionals like to use it because does not contain phosphorous, which promotes algae growth.

HEDP or 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid, strongly binds to metal ions and is commonly used as a pool sequestering agent. It is very useful to prevent scale from forming on pumps, heaters, and surfaces by binding calcium ions.

It doesn’t break down as easily as EDTA, but when it does, it forms phosphates, which is important to know if the pool also has algae issues.

One product, CuLator, made by Periodic Products, is an unusual kind of chelating agent because it is one of the few types where the metal is actually removed from the water. It is a polymer-based sequestering agent, with repeating units of hydrocarbons.

Most chelating agents stay suspended in water, but this type of chelating agent is enclosed in a packet that sits in the skimmer. The polymer package can be removed from the water once it has trapped the metals.

The product also has a color comparator chart on it so that the types of metals present in the pool or spa can be identified.

Clarifiers and Flocculants

Before using a clarifier or flocculant, it’s a better idea to try and see if you can get to the bottom of why the water is cloudy. There are a wide variety of reasons for cloudy water. These include:

• Early algae growth.

• Insufficient chlorine.

• High calcium, Total alkalinity, pH, or TDS.

• Poor filtration or circulation.

• Metals reacting with sanitizer.

• Organic contamination. The remedies for most of these are fairly obvious. If you find, however, that the problem is physical rather than chemical, use of a clarifier or flocculant may be in order.

Suspended particles are a reason for cloudy water that warrants the use of clarifiers. They are too small to be filtered, and they deflect or reflect light making the water appear cloudy. Most suspended particles are negatively charged and so they tend to repel each other, resulting in their dispersion. To capture them, it is necessary to cause them to coagulate so that they can be filtered, which can be accomplished through the use of a clarifier or flocculant.

The difference between the two terms, clarifier and flocculant, is according to some, a matter of where the coagulated particles end up. If the particles end up settling to the bottom of the pool, then a flocculant was used, whereas if they floated away to the skimmer, a clarifier was used.

The most common inorganic clarifier is alum, or aluminum sulfate, a natural salt compound and a great water clarifier. When alum and water combine, aluminum hydroxide is formed. Added to a pool, this compound tends to stick to itself, trapping small dirt particles in the process as it sinks to the floor.

Alum has been used for water clarification for centuries, and plenty of service technicians still use alum today.

To begin, the pH should be adjusted to 7.0. Most recommend using 4 pounds of alum per 10,000 gallons of water, although more can be added, depending on the amount of suspended water particulates.

It should be premixed into a slurry and added around the perimeter of the pool.

Allow the water to circulate until the filter pressure gauge goes up by 8 psi, and then allow the floc to settle. Finally, vacuum the floc to waste, and readjust the water balance.

Using alum can be a hassle, so many service technicians prefer to use synthetic organic polymer clarifiers to get the job done.

The polymers used for clarifying swimming pools are long bundles of repeating carbon units with positive charges all along their surfaces. When add to water, they form long strings with positive surface areas.

When the negatively charged dirt encounters the positively charged polymers, the opposites attract, and the dirt is drawn to the polymer.

Groups of these polymers collect together and form masses that are large enough that they can then be vacuumed or filtered out of the water by the pool’s filtration system.

There are hundreds of formulations of polymers for water clarification that have been designed for different applications or circumstances.

Some clarifiers are formulated for spas, with higher resistance to floc breakdown from the severe turbulence.

Some clarifiers are more suitable than others for specific temperatures. Some polymers can handle different pH ranges than others. And some can withstand higher chlorine levels.

One big warning before adding a polymer clarifier: Be aware if the pool water also contains a metal sequestering agent or scale remover. The polymer is positively charged while the chelating agent of the sequestering agent is negative. When the two molecules encounter one another, they bond, and the cloudy result can be almost disastrous.