Water management systems are probably the most debatable and controversial subjects in the hot tub world. First we must separate two distinct purposes of water management. The first purpose is filtration and the second is sanitation. Filtration has to do exclusively with removing organic matter and solids out of the water (typically measured in microns). This is done via a circulation pump that moves water from inside of the hot tub through filters either continuously or intermittently throughout the day. Continuous filtration also known as 24 hour filtration typically refers to a small, independent pump that circulates the water 24/7 through the filters. The small pump draws very little electricity and is quieter than a traditional jet pump. Intermittent filtration refers to a larger, jet pump that has two speeds (low and high). Low speed is used to filter the water between 4-8 hours per day (day=24hrs) moving large volumes of water through the filters. The high speed is used to run the therapy jets. There are pros and cons to each type, however, most higher end spas will typically feature a continuous, independent circulation pump. Filters have to do with improving water clarity only. They do not sanitize the hot tub water. Hot tub filters are generally round (cylindrical) and come in different sizes and densities. For example, one filter could be 8” tall and have a density of 50 square feet and another filter could be 10” tall and be only 35 square feet. It is always important to consider the overall square footage of filtration and not necessarily the size or number of filters. Some companies build their spa models with a single filter and others build them with two or three filters. Generally speaking, the higher end the spa, the more filters and square footage it will have. More doesn’t always mean better as the major difference between one or three filters just means that you will have to remove the one filter and clean it more often than if you had two or three. On the flip side, if you have three filters you may not have to clean them as often but it will cost more to replace three of them than one. Filters are generally replaced every 12-24 months depending on frequency of use and how often they are cleaned. They should be hosed off regularly and also deep cleaned every 3-6 months with a special filter cleaning degreaser.
The second purpose of water management is sanitation or disinfection. Sanitation is the most controversial as there are many sales people out there that tout their hot tubs as being chemical free which is nearly impossible. If you ever hear a salesperson say that their hot tub is 100% chemical free than you should turn around and run for the door as this is the unicorn and does not exist. If you are told such an outrageous claim and you are purchasing your hot tub on that merit then you should ask that it be provided for you in writing. The reason why a chemical free hot tub doesn’t exist is because water has many properties to it. Three of which are PH level, Alkalinity level, and Calcium Level. For water to be perfectly balanced in a hot tub so it doesn’t cause any damage to the equipment or plastics then these three properties need to be maintained in a particular range. The problem is that the water that we initially use to fill our hot tub is from our garden hose (city or well water) and it is not perfectly balanced and therefore we must adjust those levels when we fill and startup our hot tubs for the first time. Once the tub is filled and initially balanced it doesn’t mean that our maintenance stops. Because the water sits in the spa for three to six months before it is changed, things like bather load, topping off the spa when evaporation occurs, and use of sanitizers such as bromine or chlorine affect the balance levels over time and so we must monitor and adjust these levels every few weeks. More importantly sanitation has to do with making sure no bacteria is growing in your spa. The most widely accepted pool and hot tub sanitizers recommended by the EPA are chlorine and bromine. A good hot tub water management system doesn’t eliminate bromine or chlorine, however, it can reduce the amount substantially by using any of the following water purifiers (It is important to note that all four of the water purifiers below work more effectively with a dedicated, 24 hour circulation pump than a two-speed, intermittent filtration pump):
- UVC (ultraviolet light)
- Dual Generators (Ozone + UVC)
- Salt Water Generators
Ozone generators are probably the oldest, most common hot tub water purifier on the market. An ozone purifier draws oxygen from the air and runs it through an electrical current or UV light which converts the oxygen into ozone gas. Then the ozone gas mixes with the hot tub water to oxidize and kill bacteria. The ozone generator typically runs during filter cycles as the hot tub water must be circulating for it to work properly. Furthermore, an ozone generator is more effective with a continuous (24 hour) filtration system as it is able to produce ozone around the clock to kill bacterial versus intermittent cycles that run only 4-8 hours per day.
UVC generators have been around for a long time in water treatment facilities and other commercial applications, however, they are somewhat new to the hot tub industry. UVC generators emit high intensity germicidal light rays that alter and disrupt the DNA or RNA of bacteria and organisms such as algae. The electromagnetic energy from UV light also breaks down organic matter in the hot tub which prevents the buildup of harmful byproducts like chloromines and bromamines. The UVC generator runs during filters cycles just like the ozone.
Dual Generators are also new to the market. These hybrid generators use both ozone and UVC to kill bacteria making it a more effective sanitation system and thus reducing the need for bromine or chlorine even further.
Finally, we have “salt generators”. Salt water systems have become quite a buzz in recent years because they have a more natural and chemical free connotation. This is misleading because when you get down to the science of it all a salt generator is nothing more than a chlorine or bromine generator. NaCl is sodium chloride and NaBr is sodium bromide. Hot tubs generally use bromine salt generators and not chlorine salt generators because bromine is more stable at hotter temperatures which is more consistent with hot tub water. Bromide salts are dissolved into the hot tub water during the filling process and the salt water is circulated through the hot tub and converted into free bromide by way of an electrode cell that is installed in-line in the plumbing system. The cell has a mild charge running through it when turned on and it effectively splits the NaBr salts that are dissolved in the water to separate the Na and the Br thereby creating free bromine in the water to do the sanitation. The advantage of a salt generator is that it doesn’t require you to add bottled bromine or chlorine which can have impurities added to it for stability and shelf life. Those impurities can also become irritants for hot tub bathers. It is also important to note that factory installed salt water systems are almost exclusively in hot tubs. You won’t find hardly any salt water swim spas that are factory installed. If you want a salt water swim spa then you will likely have to have one installed after market.
It is also important to note that many manufacturers further supplement the aforementioned water purifiers (ozone, UVC, dual, salt) with mineral based products also referred to as mineral purifiers. These mineral purifiers come in the form of a cylindrical cartridge (approximately 1” in diameter and 5” long). These cartridges are disposable and generally last 3-4 months depending on the size of hot tub. The sticks are loaded with silver and/or copper beads that kill algae and bacteria naturally. They are usually placed inside of the filter or near the filter area so that the circulating water comes in contact with them regularly. When coupled with ozone, UVC, dual generators, or salt these catridges can achieve 90-95% bromine/chlorine free hot tub water.