In the inaugural installment of our series on Recreational Water Facility Management, we explored the interaction between chlorine and pH, examining their essential role in preserving the proper chemical balance in swimming pools and other aquatic venues.
This article advances the discussion, focusing on some of the additional elements that influence the equilibrium of water in such facilities: namely, Total Alkalinity and Calcium Hardness.
Forever Friends (Alkalinity & pH)
The first part of this article posited that, should there be an equivalent to the Oscars for maritime public health, chlorine would undoubtedly win the Academy Award for Best Chemical, with pH a strong contender for the accolade of Best Supporting Actor in a Water Production. If pH were to receive a nomination, total alkalinity would surely be its partner on the red carpet.
Although alkalinity and pH are independent, they share a significant connection. Whereas pH is an indicator of acidity by measuring the concentration of hydrogen ions, alkalinity quantifies water’s capability to neutralize acids: in simple terms, its ability to resist changes in pH.
Commonly expressed in parts per million (ppm), total alkalinity measures the concentration of alkaline substances present in water, such as hydroxides, carbonates, and bicarbonates. These specific alkaline compounds absorb hydrogen ions, which reduces the water’s acidity and increases its pH.
Total alkalinity stands out as one of the most critical yet overlooked factors in the maintenance of recreational water facilities (RWFs). It functions as a pH stabilizer, determining how resilient the water is to fluctuations in pH. Alkalinity serves as a protective buffer, shielding water from rapid pH swings that would otherwise occur from the introduction of various elements such as chemicals, precipitation, or bather pollutants.
As discussed extensively in the first part of this article, maintaining the correct pH level is crucial to ensuring chlorine’s efficacy as a disinfectant. By consistently monitoring a facility’s total alkalinity concentration, pool operators can contribute significantly to achieving this objective. Such vigilant oversight will help prevent a variety of problems and potential complications down the line.
How to Maintain Optimal Total Alkalinity
Alkalinity essentially exists in one of three possible conditions: too high, too low, or perfectly balanced. The acceptable limit in RWFs is within a range of 60 to 180 parts per million, with the optimal level somewhere between 80 and 120 ppm.
Total alkalinity can be influenced by various factors. Adding any kind of acid to an aquatic venue, such as muriatic acid or sodium bisulfate, will lower it. Indirect pollutants like sweat, urine, and sunscreen have a similar affect through the creation of acid byproducts. The incorrect use of pool chemicals and malfunctioning filtration systems can also adversely impact alkalinity levels. If an RWF is located on an open deck, abrupt changes in temperature and rainwater are additional considerations to be aware of.
Insufficient total alkalinity can cause a range of problems. These include dramatic shifts in pH when chemicals or pollutants are introduced into the water, as well as operational challenges to consistently maintain and stabilize pH within its required range. Additionally, when combined with a low pH, other effects such as the corrosion and etching of pool surfaces and equipment, along with an increased consumption of disinfectants (e.g., chlorine) may be observed.
When the total alkalinity is too low, adding sodium bicarbonate will raise it. Alternatively, sodium carbonate can also be used to elevate a pool’s alkalinity; however, it should be noted that this method will concurrently increase the water’s pH. This dual effect can be beneficial, however, when there is a need to raise both total alkalinity and pH.
Conversely, when total alkalinity is too high, the enhanced effect of its “protective buffer” makes it difficult to adjust the water’s pH. As a result, the pH levels in an RWF tend to gradually increase over time, triggering a series of other problems such as cloudy water, scale deposits, filtration system issues, and the reduced sanitizing power of chlorine.
Total alkalinity can be lowered by the introduction of an acid. Even so, this process can be challenging as adding an acid to the water will also cause a drop in pH. While some acidic-based products may reduce alkalinity more significantly than they affect pH, the process typically involves a repetitive cycle of decreasing alkalinity followed by subsequent adjustments to raise the pH.
Muriatic acid, commonly known as hydrochloric acid, is often the most practical choice to reduce alkalinity levels in RWFs. The chemical reaction of muriatic acid with alkaline substances in the water results in the formation of sodium chloride (NaCl), carbon dioxide (CO₂), and water (H₂O). This process reduces total alkalinity and, consequently, lowers pH. Essentially, acids work by “neutralizing” total alkalinity; in other words, by burning away the pH buffer.
In cases where pH is low and total alkalinity is high, raise the pH first into the required range and then lower the total alkalinity. Reverse this process when the total alkalinity is low and the pH is high.
Maintaining a stable pH level in recreational water facilities is essential for bather safety, and total alkalinity plays a significant role in this process. As alkalinity lacks its own stabilizing agent—pH gets the greater benefit from their relationship—alkalinity levels tend to be more prone to fluctuations. Minor deviations do not in themselves pose an immediate health risk, but are an indication of potential issues with water balance management.
Effective alkalinity control requires incorporating regular weekly testing into a facility’s maintenance regime and taking prompt action when results fall outside the required range. This approach does, however, apply to all elements of RWF water chemistry, not only total alkalinity.
What is Calcium Hardness?
After meticulously adjusting the free chlorine residual, pH, and alkalinity levels in your RWF, calcium hardness emerges as an unforeseen factor that can disrupt the equilibrium.
Calcium hardness refers to the total concentration of dissolved calcium, in conjunction with other minerals such as magnesium, in pool water. When calcium levels deviate from their ideal range, it can trigger a domino effect of other chemical imbalances that may ultimately damage a pool’s surfaces and equipment, decreasing the lifespan of machinery and associated components.
According to the latest Model Aquatic Health Code (MAHC) recommendations, calcium hardness levels should not exceed 2500 ppm. For RWFs with water temperatures less than 32°C (90°F), the optimum range is 200-400 ppm. In venues where this temperature is exceeded, the MAHC code suggests calcium hardness should be between 100 to 200 ppm.
When calcium hardness levels are insufficient, especially when combined with low pH or total alkalinity, the water gradually becomes “aggressive”. This causes corrosion and staining of a facility’s infrastructure, and discoloration of the water itself. Corrosive water compensates for a lack of minerals—in this instance, calcium—by extracting them from alternative sources such as the lining of a pool.
Insufficient levels of calcium may result from:
- The effects of weather (e.g., rain or snow)
- Overuse of products containing hydrogen peroxides, such as chlorine tablets or shock treatment
- Algae
- High levels of metals such as iron or lead in the source water
On the other side of the coin, excessive calcium hardness leads to the formation of calcium deposits, commonly referred to as scale. This occurs as a consequence of the calcium ions reacting with bicarbonate alkalinity in the water, resulting in the creation of calcium carbonate (CaCO3)—a white, insoluble solid that determines the softness or hardness of water.
The accumulation of scale on machinery and plumbing components will increase maintenance requirements and, in extreme cases, may require damaged pool equipment to be replaced. Moreover, high calcium hardness can result in turbidity issues (cloudy water) which typically manifest when both a pool’s total alkalinity and pH levels are simultaneously elevated.
High levels of calcium can be caused by:
- Adding too much calcium chloride (CaCl2) or calcium hypochlorite (CaOCl2) to the water
- The use of an acid cleaners like sodium chloride
- Chlorine tablets, shock treatment, or water conditioners with high levels of calcium
How to Fix Calcium Hardness Issues
The optimal level of calcium hardness is achieved when the water is in a state of equilibrium, neither under-saturated nor over-saturated. The good news is, with calcium hardness, there’s quite a bit of leeway.
In reality, determining the ideal calcium hardness for a particular RWF is influenced by a multitude of factors. These include what materials were used in the facility’s construction and whether it’s filled with saltwater or fresh water. Additionally, the location of both the venue and the ship itself can play a role.
For example, for ships sailing in warm, sunny climates with open deck pools, the process of water evaporation can significantly increase calcium hardness. As water evaporates, the calcium ions (and other minerals) dissolved within it remain behind: a process that results in a higher concentration of calcium carbonate, leading to increased hardness levels. This phenomenon is similar to the buildup of mineral deposits observable on a vessel’s showerheads.
As with total alkalinity, deviations in calcium hardness—even up to 300,000 ppm—do not pose an immediate health risk to bathers. Nonetheless, insufficient or excessive calcium levels indicate that the water balance in an RWF is not being properly maintained, signaling the need for a detailed review of management practices.
As calcium hardness tends to be a more stable factor than chlorine or pH, the same frequency of monitoring is not required. For most RWFs on board, monthly testing should be sufficient.
In aquatic venues such as whirlpools spas and baby-only water facilities, which must be completely drained and refilled at least every 72 hours on cruise ships, calcium hardness seldom causes problems. However, in facilities that aren’t regularly drained, such as fresh water swimming pools, it’s important to check and adjust levels to prevent water quality issues and potential damage to the venue’s structure and equipment.
Before adjusting calcium hardness, it’s essential to first address the total alkalinity and pH of the water: in that order. This sequence is crucial because changes in alkalinity can affect pH. Similarly, when both alkalinity and pH are adjusted, they can indirectly influence calcium hardness due to the fact that certain chemicals used in the process, like sodium bicarbonate, often increase the hardness of the water. Thus, tackle alkalinity first, then pH, and finally, calcium hardness to maintain optimal water quality.
Raising the calcium hardness level is much easier than reducing it. To elevate calcium levels, consider using a hardness increaser such as calcium chloride. This particular compound is designed to increase calcium hardness without altering the other characteristics of the water. Caution is key when using calcium chloride as overdosing can lead to complications that are more difficult to resolve than low calcium hardness. To ensure precise measurements, there are numerous online resources available to support pool operators, including the Pool Advisor’s Calcium Hardness Calculator.
Dealing with excessively high calcium hardness is particularly challenging, as it’s one of the few recreational water issues that cannot be simply resolved by adding more chemicals. The most effective solution is to completely empty a facility and refill it, however, this can be an expensive option depending on the volume of water the venue holds. A more economical alternative is to partially drain the RWF and top it up with fresh water, although the success of this venture depends on the water added having a low calcium content.
Draining and refilling an RWF doesn’t just adjust the calcium concentration; it alters all aspects of the water’s chemical composition. Consequently, it’s essential to conduct a comprehensive analysis upon completion, which should encompass tests for free chlorine residual, pH, total alkalinity, and calcium hardness. Pool operators must be prepared for some rebalancing to the water chemistry of the facility to restore optimal conditions.
More often than not, excessive calcium can be traced back to water that is not been correctly balanced. Common factors that contribute to this include high pH, water evaporation, and temperature—factors that, along with total dissolved solids, will be explored in the third and final part of this article.