Swimming Pool Blog


How's Your Filter? The Trio - Part III


by Rob, October 31, 2008 

Welcome to part III in the series called The Trio. Our first two parts focused on Filtration and Circulation as key components to clean, clear pool water. The third and final installment will focus on Sanitation.
 
So, what is Sanitation of pool water? According to Wikipedia Swimming pool sanitation refers to both visual clarity and levels of microflora, such as bacteria and viruses in swimming pools. The goal of sanitation is to prevent the spread of diseases and pathogens between users. Unsanitized water may also support the growth of algae which will present as a greenish tinge initially, then if left unchecked may completely inhabit the pool water displaying a solid green murky appearance.
 
Chlorine, in tablet form, is the primary sanitizer used in modern swimming pools. Without a proper level of disinfectant such as Chlorine, all sorts of bacteria such as E. Coli or Staph or Pseudomonas can live, and can spread from person to person in a swimming pool or spa. Proper levels of Chlorine or Bromine of at least 1.0 part per million will kill most bacteria and viruses that can live in the water.
 
But what if our "halogen residual" or level of chlorine should drop to near zero? Well, then the contaminants will begin to bloom again. Although important to keep a near constant level of sanitation in the pool - if the level does slip we will likely first begin to see the water become cloudy or hazy after a day or two, becoming progressively more so as time goes on. Algae will likely show up next, and continue to grow towards swamp like conditions, which may contain pathogens or disease causing organisms. Filtration and Circulation will slow this transformation, but without proper pool water sanitation, a swamp is an inevitable result.
 
Using a powdered or granular form of chlorine, also known as 'shock" can be useful to bring up a chlorine residual fast. Liquid chlorine, where available, is also rapidly dispersed through the pool water when added.
 
It should be noted that the Trio of Filtration, Circulation and Sanitation work together to keep your pool water clean and clear. In concert with each other, each component does it's part. As extreme examples, if you used, say, 5 gallons of liquid chlorine per day, or 5 lbs of granular shock per day - you could have clean and clear water without much filtration or circulation at all! Conversely, you could have a filter as big as a house, and over-filter the water so much, that chlorine may not be required. Or - circulate the water, at 1,000 gpm (gallons per minute) and not need filtration or sanitation. But, in the real world, we try to strike a balance between all 3 components.
 
Also important in the discussion of Sanitation is the pH level of the water. The active molecule of Free Chlorine, loses much of its potential at higher pH levels. Higher pH levels, above 7.6, reduces the efficacy or killing power of chlorine, due to lower Oxidation-Reduction Potential (ORP). Low pH has an opposite effect, exciting the molecule into a ravenous contaminant assassin! However - pH levels below 7.2 are considered "aggressive" in a pool environment, and can lead to erosion of pool surface finishes like plaster and vinyl, loss of chrome finish to ladders and lights, as well as bather eye and skin discomfort. So, to get the most "bang for your buck" with your chlorine, keep your pH level at 7.2-7.4.
 
A good test kit is also important, to check and maintain pH and chlorine levels. I'm sorry, but I don't like test strips....they are too easy to mis-read, and my old eyes cannot tell the difference between 7.2 and 7.6 on the pH scale, or 1.0ppm of chlorine, or is it 2.0? Hard to tell. Using a fresh dropper style test kit for pH and Chlorine is recommended. It can save you money by keeping your chlorine level close to 1.0ppm and keeping your pH level down, so the Chlorine works well. If your chlorine level is 2.0ppm - you may be spending twice as much money on chlorine than you need to! So use a good test kit, and test often.
 
Speaking of test kits, a test kit will tell you how much Chlorine to use on any particular pool. Every pool has a unique "Chlorine Demand" - meaning that every pool will need to use slightly different amounts of chlorine to achieve 1.0ppm. Why? Some of the variables include size of pool, size of filter, run time of filter, bather load (number of swimmers), amount of organic matter invading our aquatic environment (lots of trees around the pool), temperature of the water, amount of sunlight or shade, etc.
 
So, with a bit of daily chlorine level testing, you can establish the number of tablets needed to build and maintain a 1.0ppm residual of chlorine. For example, put 2-3 tablets in your chlorinator or chlorine floater. Then test the water after 24 hours. If the level is too high, then you can remove 1 of the tablets, or turn the dial down on the chlorinator or close the openings some on the floater. As the tablets dissolve and get smaller, there will be less chlorine entering the water. After a number of days, they will dissolve completely and need to be replaced. With a bit of experimentation, you can "dial-in" the correct amount of chlorine to use for your pool, at any given time of year.
 
For some users of a chlorinator, they may have a lower dial setting when the chlorinator is full, but as the tablets dissolve it may become necessary to increase the dial setting to maintain a constant level of chlorine in the pool.
 
For those with more seasonal pools, less chlorine will be required during the cooler parts of the year. You may find the Chlorine Demand in August to be twice that required in April. This is due to higher water temperature, and presumably higher pool use.
 
A properly sanitized pool will have no chlorine smell. If you smell a strong chlorine odor around the pool, this is usually misunderstood and thought to be caused by too much chlorine in the pool. Free Chlorine molecules actually have no smell or taste, and are in their most potent state. Chloramines, on the other hand, are foul smelling and irritating to skin and eyes.
 
Chloramines, also called Combined Chlorine Molecules, are chlorine molecules combined with nitrogen or ammonia. They lose their ability to sanitize effectively, have a strong chlorine smell and burn the eyes. Sounds strange, but the recipe to fix this problem is to put in a whole bunch more chlorine, to break apart these combined chlorine molecules, and return your pool to mountain spring fresh.
 
To "Shock" a pool properly, one needs to add enough chlorine to reach a threshold called "breakpoint chlorination". At this very high level of chlorine, everything is oxidized, or basically destroyed, on a molecular level. Molecular bonds are broken and cell structures are ripped open - sort of like a lightning bolt slashing through the water. At least that's how I like to think of it.
 
A discussion on sanitation of pools would not be complete without some mention of alternative sanitizers. It is extremely difficult to operate a swimming pool without some form of halogen, i.e., Chlorine or Bromine. However, one can dramatically reduce their reliance on or use of Chlorine or Bromine with the use of one of the following methods of Alternative Sanitation:
  • Ionization Systems - Use of Silver and Copper ions - which are effective algaestats and bacteristats, respectively. Some systems are electrically charged and some, such as Nature2, use replacement cartridges.
  • Ozonation Systems - Ozone is an extremely powerful sanitizer, but it's hard to get the little nascent atom in contact with much of the water for complete sanitation. Very popular in spas and hot tubs.
  • UV Systems - Ultra Violet light! Just run water by a UV bulb and certain pathogens and contaminants are killed. Also popular in spas and hot tubs.
  • Biguanides - Soft Swim and Baquacil are popular brands of this peroxide based pool sanitizer. This is the only system that can be used if you want to completely eliminate the use of chlorine in your pool.
Of course, there is always UltraFiltration, as a method of sanitation - not very practical in pools (think filter as big as a house). We need to strike a balance in our use of Filtration, Circulation and Sanitation to keep our pools clean and clear.
 
So, here we are - Full Circle. When addressing water quality in your pool, remember to attack the problem with the triple edge sword. Consider all variables of your Filter, Pump and Chlorinator, and how they work together, in concert, for proper Filtration, Circulation and Sanitation.
 
Yours Pool-y!
 
Rob