Since 1990, HydroTher Hot Tubs have been the #1 choice of architects, consultants, designers and facility operators for commercial aquatic applications.
With salt chlorine generators now being widely used for pool water treatment, their use in spas and swim spas is rapidly on the rise. More spa and swim spa customers are choosing salt chlorine generators because they already have them on their pools, or they have learned about them being an option. At the end of the day, most owners want to spend less time performing maintenance, and these devices allow that. Salt chlorine generators on pools are very similar to those for spas, however, regardless of their similarities, there are steps that should be taken to maximize the benefits and minimize the side effects of such generators.
After the generator itself, salt is the most critical component in making a generator produce the vital chlorine to keep water safe for bathers. Generators for pools typically need the water to contain around 3000 parts per million (ppm); in spas, these devices require around 2000 ppm of salt. However, each of these are estimates and the manufacturer should be consulted for their own target ranges for ideal performance results. Regardless, it is important to note, approximately 0.19 kg (0.42 lbs) of salt introduces 100 ppm of salt for every 1892 L (500 gal) of water.
Finding phosphates in water
Being mindful of the makeup of the source water of the spa is even more important when a generator is equipped in the facility. Well water may have iron present in it, and this can quickly interact with a cell generator and create water discolouration or stains. Ideally, a filter attached to the source water, whether in the home or at the end of the garden hose, is a necessity to remove metals. Alternatively, top loading water with metal treatments containing phosphonic acid should be avoided or at least proceeded with caution, this article will expand on this later. Further, there are also common issues that most water sources face, such as elevated total alkalinity (TA) or saturated calcium levels.
City water may have its own problems when being used to fill spas with generators. Often in the United States, polyphosphates such as sodium hexametaphosphate (SHMP), sodium tripolyphosphate (STP), or tetrasodium pyrophosphate (TSPP) are used to control common metals from causing issues within a potable water system. Regardless of which flavour it arrives in, all these water treatments will introduce phosphate to water at various rates.
In most cases, the introduction of phosphates in traditionally treated spas, especially spas which are covered when not in use, will never be an issue. Phosphates are already “fully oxidized” in water and have no impact on the performance of common oxidizers typically introduced to water. Such oxidizers include chlorine (in any form) and oxidizing shocks, such as potassium monopersulfate (KMPS). However, when a spa is equipped with a generator, excess phosphates may interfere in the generator’s ability to reliably produce chlorine.
Previously mentioned was the use of phosphonic acid to control metals in spa water. These acids work well to rid metals from water, or at least reduce the visual impact of metals in water. However, use of these products will also introduce phosphate to water. Sometimes the use of these agents is necessary to solve harder problems, but the use of such chemistries should be avoided on a continuous basis.
Filtering out phosphate in water
Preventing the introduction of phosphate from the source water or with the use of metal agents would be an ideal scenario, however, options for filtering out the phosphate in the filling stage are limited. When filtration is not an option, phosphate reducing agents are the next best solution. When reducing phosphates in spa water, gradually reducing the levels in the water is perhaps the best method, as it would avoid making the water turbid. Alternatively, reducing phosphate levels too quickly can cause the water to turn cloudy. In either case, the resulting precipitate allows the filter to capture phosphate. As a result, removing the filter and rinsing it is critical to removing phosphate or else it never leaves the water.
Spa and pool water maintenance
As with pools, a common headache of using a chlorine generator in a spa is keeping the pH in the preferred parameters. The constant rise of the pH from the cell operating is accelerated by the aeration of water from simply using a facility’s jet pumps or bubbler system. Ultimately, testing and adjusting the spa water more often is the remedy, which is the opposite of what spa owners are looking for, and that is more maintenance. The introduction of borate to spa water will introduce a secondary buffer system, and the net result, for most, will reduce the frequency where the pH and the alkalinity will need to be adjusted.
Fortunately, when it comes to spa care maintenance, there is not much work to be done to the equipment itself. Filters requires their own care and dedication, so they perform their function adequately and last as long as possible. Further, spa salt cell generators do need to have their cells replaced or cleaned at least yearly to keep producing chlorine. Since spa generators do not have as much output as a generator for a pool—a vinegar solution, or even some spa filter cleaning solutions should be sufficient to clean the plates of the generator. As always, preventing any type of buildups, such as scale, is key to ensuring the life of the spa equipment—and generating cells are no exception either. Adding borate to spa water can help extend the life of those components as well.
It is very important to provide a chemical treatment that is specific to spas with salt chorine generators, the spa water temperature, and the use and bather load. Using one or more of the tips above will assure satisfaction for all parties involved. Training staff and clients on the differences in spa water treatment in spas, compared to swim spas with salt chlorine generators is key to the clients’ long-term satisfaction with to a spa.
Pro tips for service providers
To ensure the overall wellness of the clients’ hot tubs, the following are a few tips for service professionals to keep in mind.
Service tip #1
The Centers for Disease Control and Prevention (CDC) recommends checking and adjusting hot tub chemicals every hour when bather load is high to make sure chlorine is at 2 to 4 ppm and the pH level is 7.2 to 7.8. In the case of bromine, the sanitizer levels should be between 4 and 6 ppm.
Service tip #2
Service technicians should include a note on their maintenance checklist to scrub off any slimy bacteria (biofilm) appearing on hot tub walls, so it does not continue to circulate in the water.
Service tip #3
One should also make a note of the installation date and any hardware changes or major repairs on the customer record. Many newer hot tubs come from the factory or have options to add secondary disinfection devices, which can help improve the water quality and lessen the amount of maintenance work. This being said, these devices require regular upkeep that is often overlooked, such as replacing solarized ultraviolet (UV) bulbs, or replacing an ozonator as they have a limited lifespan.
Service tip #4
Create a laminated checklist for new and existing hot tub owners. Many technicians are now leaving a laminated ‘enter-exit-checklist’ attached to hot tub covers. This encourages users to check sanitizer and disinfectant levels as they open and close the hot tub when they enter and exit the vessel. Note, it is important water balance parameters are in range, and enough sanitizer is present in the water.
Service tip #5
Oxidizing with a non-chlorinated shock is very important because those soaking in the spa can excrete up to one pint of fluid every 30 minutes, sweating in the heat of the water. It is also very important to leave the cover off for a minimum of 30 minutes to allow for gas off after adding the oxidizer. Be sure to also use a high quality, broad spectrum enzyme weekly to help maintain a healthy environment. This will also help break down the organics that were introduced for the oxidizers to work more efficiently.
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