Clearing The Water

What happens when a routine water analysis indicates the water in a swimming pool or hot tub is chemically balanced, but the water appears less than perfect?

Too often a pool operator’s solution is to blindly add more chemicals and perform unscheduled maintenance on equipment, which can waste precious time and money. Additional testing is often forgotten about unless it is to verify the initial result.

Performing a secondary test can easily identify the root problem, making treatment more simple and cost-effective.

Let’s assume that primary routine testing includes chlorine (free and total), pH, total alkalinity, total hardness and cyanuric acid (for outdoor pools). Although not performed as frequently, cyanuric acid and hardness testing are certainly of primary importance, and should be performed on a regular basis. Additionally, if a swimming pool is maintained with phosphate-removal chemicals, the testing of phosphates is also of primary importance.

Other testing is considered secondary, and often gets overlooked. Therefore, if all of the regular primary tests appear to be within specification, yet the water is still less than optimal, it is time to consider some of these secondary tests. Here are a few of the most common to consider:

• Nitrates

• Metals

• Total dissolved solids


Nitrate is a nitrogen compound that forms naturally in the soil and atmosphere, and can also be present in water. Having nitrate contamination is like hosting rude in-laws during the holidays--they never leave quickly enough, and getting rid of them is hard to do. Nitrate nitrogen is extremely stable in water. As a result, its stay in pool or spa water can be an extended one.

Nitrates can be introduced to water through a number of sources. The water used to fill the swimming pool or hot tub may contain nitrates, especially if well water is used.

Fertilizer is another common source of nitrate intrusion. Many fertilizers contain a high level of nitrate nitrogen to keep lawns and plants plush and green--obviously not the ideal color for a swimming pool. Nitrogen from fertilizers can be washed into the swimming pool by rain, wind, bathers or animals, or can result from the overspray of an overzealous lawn service or golf-course maintenance person.

Other sources of nitrate nitrogen are human and animal wastes, rain, leaves or other decaying plantlife.

Any one source can introduce a significant numbers of nitrates into the water. However, a problematic buildup can occur over time as a source continuously contributes nitrates. Likewise, a combination of these sources may build up even more quickly, which can have an even greater impact on water quality.

Why it should be tested: In well-balanced water, nitrates will increase sanitizer demand, causing water to require higher-than-normal dosages of chlorine, bromine or other sanitizers.

Even a small amount of nitrate -- around 10 parts per million (ppm) -- can affect the sanitizer demand. Algae can also become an issue with high nitrate levels.

Algae in a pool love nitrates like a teen loves texting. Algae may become uncontrollable in the presence of a high nitrate supply, even if there is enough sanitizer in the water to prevent algae.

The ideal range of results: Testing for nitrate levels in advance of treatment will determine whether continuing to treat the pool by adding more chlorine will be effective, or if a partial drain and refill will be more practical.

If the nitrate level in the water is below 10 ppm, you should be able to control it with regular treatment, which may include regular algaecide dosage. If it’s above 10 ppm, consider the cost of fresh water.

The only practical way to lower the nitrate level above 20 ppm is to drain and refill the pool with water that contains no nitrates (or a very low number). In most cases, this can be accomplished with a partial drain and refill.

Metals (Typically Iron And Copper)

Copper and iron are the two most common problem metals for swimming pools and spas. While both metals are needed to maintain a healthy diet, neither is desirable in a swimming pool or hot tub.

Again, the most common origin of copper and iron in pools and spas comes from the source water. Water erodes and dissolves metals underground, and over time it makes its way into wells or other water supplies. Pipes or other metal equipment can corrode, particularly if the pH or hardness level of the source water is too low.

Additionally, some algaecides use copper as an active ingredient, as do certain mineral purification systems.

Why it should be tested: Once metals have found their way into a pool, these water intruders can contribute to discoloration and scaling, even in otherwise properly balanced water. Pool water, with a greater exposure to air, changes (oxidizes) the iron in the water into a yellow or reddish-brown solid. Copper tends to turn into a blue or bluish-green color.

When these metals settle out of water into their solid form, they cause stains and rust on pool surfaces, fixtures and equipment. Smaller particles remain suspended in the water, causing a color change.

The ideal range of results: Maintaining a low copper level at or below 0.2 ppm can prevent the formation of scale deposits or stains.

Total Dissolved Solids (TDS)

Knowledgeable swimming pool operators know that seemingly balanced water can still be aggressive or scale-forming. A quick calculation of the Langelier Saturation Index will show this. While the explanation of the Langelier Index would take another article, I will focus on one of the primary factors of the index--Total Dissolved Solids (TDS).

TDS is a measure of the total amount of dissolved matter in water. This includes calcium, magnesium, carbonates, bicarbonates, metallic compounds, etc. Every time chemicals are added to the water, TDS is added in one form or another.

Why it should be tested: Over time, TDS levels build up as more chemicals are added and leftover salts, minerals, etc., remain. When all of the standard tests appear ideal yet the water has become dull, or ideal levels are difficult to maintain, check the TDS level.

High pool or spa TDS levels can result in hazy water, dull water, fixture corrosion or scale buildup. High levels can also reduce the efficiency of other chemicals present, including the sanitizer.

The ideal range of results: For proper swimming pool and spa maintenance, TDS levels should be no more than 1,500 ppm above the initial fill level. That means whatever the TDS is at the initial startup of the swimming pool or spa, do not allow more than 1,500 additional ppm before draining and refilling.

A partial drain and refill may be all that is necessary to lower the TDS level.

Remembering these secondary tests the next time there’s a problem can save important time and money, not to mention lessening the headache of trying to solve the problem blindly. Keep a test kit on hand, and make sure you understand the problem before trying to trying to find a solution.

Joe Sweazy is Technical Sales and Services Manager for HACH Company/ETS Business Unit, manufacturer of AquaChek and other water-quality products in use around the world. He has published more than a dozen articles on pool and spa water chemistry, and has presented numerous seminars at conferences of the Association for Pool and Spa Professionals (APSP) and at the World Aquatic Health Conference. He may be reached at

Bryan BuchkoComment