By Terry Arko
Why do people buy hot tubs? Is it because they want to pretend to be chemical engineers and chemists? The answer is obvious. People buy hot tubs because they want to relax and relieve stress. They want to soak in hot, bubbling water and ease away their worries, at least for awhile. So, most incipient hot-tub owners always flinch when they hear terms like sanitizer residual and water balance. And most are resistant and confused when it comes to the care that can be involved with keeping hot-tub water clean and clear. Following are some simple steps for hot-tub water care that can help anyone through the process of making water better in their tubs.
Know your source
The first and most vital part of hot tub water care is to know what type of water is being put into the hot tub from the first filling. It is important to know the make-up of the water that will be put into the hot tub. Does the water come from a well or is it city water? Is the water hard or soft? What is the TDS reading in the source water? These questions should be addressed even before the hot tub is delivered and chemicals are sold, in order to know what is needed for the start-up process. For example, if the hot tub is in the Seattle, WA area, the source water is naturally very soft, meaning it has very little mineral content. Water is a universal solvent and will always seek to find a balance. Water seeks to have a certain amount of calcium mineral to achieve equilibrium and/or a non-aggressive state.
When naturally soft water is introduced into a hot tub, it must have some additional calcium introduced in order to give the water enough saturation to prevent it from being aggressive and causing corrosion of metal parts. For this reason, a chemical called calcium chloride is used to give the water a balanced saturation level. In contrast to this would be an area like Phoenix, AZ, where groundwater may have been taking up calcium and magnesium from underground limestone formations for hundreds of years. That source water will be naturally hard, meaning it has a high calcium and magnesium content. In this case, at start-up, no additional calcium supplement will be required. In either case, water should always be tested for total hardness first to determine if calcium chloride is required to achieve the recommended level for total hardness in hot tub water between 200 to 400 ppm (11.7 to 23.4 grains per gallon).
It’s all about balance
Next, the water needs to be balanced. Apart from adjusting total hardness, there are two other important factors that need to be adjusted to ensure proper sanitizer effectiveness and protection of equipment: total alkalinity and pH. Proper total alkalinity gives the water a buffer to resist fluctuation from the addition of other chemicals, such as sanitizers and shock treatments; pH is a measurement of hydrogen ion in the water and is used to measure the level of acids or bases. Between the two balance adjustments, total alkalinity is the first and most important adjustment to be made. Many people confuse total alkalinity and pH, thinking they are the same and that as long as pH is adjusted, total alkalinity is adjusted, too. This is a faulty premise, as total alkalinity and pH are not the same but are related. The purpose of total alkalinity is to act as a buffer to resist changes in the pH; total alkalinity must be in the proper range in order to keep the pH steady and at its correct level.
If total alkalinity is too low, there will not be enough buffering ions in the water to hold the pH steady and it will rise and fall dramatically, according to whatever is introduced into the water. This could be other chemicals, bather waste or byproducts from sanitizing or shocking chemicals. If total alkalinity is too high, pH is very hard to adjust, as it is held captive by the buffering ions.
Water is all about balance. Having total alkalinity and pH at the proper ranges will make the overall water quality much better and ease of maintenance much easier. Total alkalinity should be between 80 and 140 ppm; ideal total alkalinity in a hot tub is 120 ppm. pH should be between 7.2 to 7.8; the ideal level is 7.4. If total alkalinity and pH are too low, a sodium bicarbonate-based enhancer can be added to the water to raise both total alkalinity and pH. To lower total alkalinity and pH in hot tubs, sodium bisulfate (a mild granular acid) can be used. Muriatic acid should not be used in a hot tub as it can be too aggressive in a small body of water and cause corrosion problems. Always test and adjust total alkalinity first. When total alkalinity is properly adjusted, the pH may follow suit on its own. Always adjust the water balance gradually, adding just what is needed and test between each chemical adjustment.
Time to sanitize
Now that the water has been balanced, it’s time to add sanitizer. There are numerous products for disinfecting hot tub water but the two most commonly used are still chlorine and bromine. The most common form of chlorine used for hot tubs is sodium di-chlor. It is preferred primarily because it is a fast dissolving granular with a near neutral pH of 6. When using sanitizers in a hot tub, it is important to use chemicals that exhibit the least effect on total alkalinity and pH. Many chemicals are designed for swimming pool use and should not be used in a hot tub. Because a hot tub is a very a small volume of water compared to a swimming pool, pool chemicals have a tendency to throw the hot tub water out of balance. One example would be liquid chlorine, which has a pH of 13 and is very high in alkaline salt content. When liquid chlorine is added to a small hot tub, both alkalinity and pH will be increased; an acid will be needed to adjust the balance back down. It is always better to treat hot tub water with the proper chemicals to obtain the greatest effect from the least amount of chemical. Chemicals that are formulated specifically for hot tub use are designed to work in smaller bodies of water that have a higher saturation rate.
Bromine is a cousin to chlorine; they are both halogens and both do a great job at killing bacteria in hot tub water. Bromine is often preferred because it has the ability to hold a residual in heated water longer than chlorine. Chlorine will begin to gas off and dissipate at temperatures in the high 80s (F). Bromine, however, will hold up to 104ºF (40ºC). Bromine is also more convenient; it comes in erosion-type tablets that can be put into automatic feeders or floaters in the hot tub. Chlorine, on the other hand, must be added manually and frequently to ensure a proper residual of protection in the water from bacteria. Chlorine should be maintained at 3 ppm, while bromine should be between 3 and 5 ppm.
Shock and maintain
Once water is balanced and the sanitizer is set, it’s simply a matter of maintenance. This doesn’t mean that the hot tub owner must have a plethora of bottled chemicals on the shelf to maintain the water. Overall, there are really only two other items needed besides water balancers and sanitizers: a non-chlorine oxidizer (known as shock) and a good natural-based water clarifier (known as a flocculant). Natural flocculants are better in hot tubs because they contain no petroleum-like synthetic clarifiers. Oils in hot tubs can combine with dirt and create unsightly scum lines and clog filters. It is highly recommend at least weekly to oxidize or shock using a buffered form of potassium monopersulfate. The shock should be marked as ‘buffered’ on the label. This simply means that it contains chemical buffers added to neutralize its naturally acidic make up. Again, pool forms of shock should not be used as they are not buffered and will lower pH. The main reason for weekly shock is to help remove non-living, organic-based contaminants from the water so that chlorine or bromine aren’t consumed trying to accomplish the same thing. Remember, the main job of a sanitizer in hot tub water is to kill germs or disinfect. Regular shocking with a non-chlorine oxidizer helps to ensure the greatest effect from the sanitizer, whether it be chlorine or bromine. Lastly, most hot tubs have a cartridge filtration system that is capable of removing particles down to 15 microns. Particles smaller than 15 micron will continue to pass through the filter. As particles accumulate, the water becomes hazy and dull looking due to charge-to-charge repulsion. A natural clarifier possesses a long-chain molecule of an opposite charge that grabs the small micron particles and creates a larger floc, which is now filterable. Thus, the water is clarified and the filter is able to better remove small micron waste.
In a nutshell, simple hot tub care involves knowing the source water, balancing, sanitizing, weekly shocking and clarifying. When these simple steps are carried out, the water will stay clean and inviting. Perfect for relaxing away the stress of the day!
About the author
Terry Arko has over 30 years experience in the swimming pool and hot tub industry. He has worked in service, repair, retail sales and chemical manufacturing and has extensive experience in customer service, sales and product development. Arko is both a Certified Pool Operator (CPO) and CPO course instructor through the National Swimming Pool Foundation® (NSPF®). He has authored over 50 published articles on water chemistry and is a popular speaker at many industry trade show events. Arko authored “Book on Water Chemistry”, published in 2005 by Halosource, Inc. and currently works with SeaKlear Recreational Water, a division of Halosource, Inc. He can be reached at (425) 974-1943 or by email at firstname.lastname@example.org
About the company
Bothell, WA-based Halosource creates technologies to make all water better. This includes drinking, environmental and recreational waters.