Lesson 5 - Disinfection

    Disinfection goes hand in hand with filtration to keep your pool water sparkling clean and clear. One is not more important than the other, and neither by itself will produce perfect results. 

    The bottom line is this. It is entirely possible to render your pool water organically inert or lifeless. But that doesn't mean the water will be clean and clear. It may be so cloudy you can't see the main drain. Only the filter can remove particulates. On the flip side, you could have water that has been filtered so that 10-micron sized particles have all been removed, and yet the water may contain unseen bacterial, viral or fungal contaminants that make it undesirable for swimming.

    Let's say disinfection and filtration are two sides of the same coin. Yet they are not the same thing, so we'll cover them separately. Lesson 6 - Filtration should be read as well.

    Disinfection is a bit of a misnomer since we don't think of pool water as being 'infected' really. Terms we commonly use to describe water quality include clean, clear, green, cloudy, swimmable, and so on. But not infected. Often the topic is referred to as Sanitizing. I'll use 'sanitize' and 'disinfect' interchangeably. Remember, these lessons are designed with new pool owners in mind, not a dissertation committee. More detailed information can be found in books such as the publications in the Library section.

    With that in mind, disinfection is a term we use when we want to describe the process of killing everything living in the water. From the lowliest germ, bacteria and algae - all the way up the food chain to include fish, frogs and the (seemingly indestructible) water bug - the goal of disinfection is to make the water a chemically undesirable place for anything to live. Yet it can't be so toxic that you and your kids can't swim in it, and occasionally swallow a mouthful.

    This can be done several ways. Chemicals like chlorine and hydrogen peroxide are added directly to the water to kill micro organisms on contact; metals such as silver and copper are used in devices that ionize or 'zap' the water as it passes; ozone generators inject ozone into the water which lasts for about 20 minutes. 

    Some of these methods can be used together, some cannot. All have pluses and minuses, whether it's cost, effectiveness, simplicity or some other criteria. You'll want to talk to a pool professional to see everything that is available for your pool. Since chlorine disinfection is so popular, let me spend a few minutes on it. If you need an explanation of how chlorine works, please read the chlorine story.

    Chlorine is the most widely used chemical for sanitizing swimming pool water in this country. Many if not most municipalities use chlorine to treat drinking water. (I understand that in Europe municipalities use ozone more than we do here.) I always ask new pool owners to use their pool test kit to test the tap water in their homes. Such a test is good practice, but it also lets you see what you are drinking and adding to your pool. 

    Chlorine is actually a green gas although we usually purchase as a white powder or in tablet form. If you look at a cup of bleach held up to the light, you will notice a slight green tint of color. Chlorine is poisonous, corrosive and it is an oxidizer. But it is also an effective bacterial, fungicidal, algaecidal control agent when used properly in swimming pools. (For more on chemical safety click here.)

    In a room filled with chlorine gas, you wouldn't live very long. If you leave a bucket of chlorine tablets or powder in your car trunk, a nice coat of rust will form on all the metal surfaces. If you allow a bucket to sit out in the rain, even with the lid on tightly, dry chlorine can become damp and release the gas. Thus when opening a chlorine container, be careful not to inhale until you know it is safe. If you see a greenish or yellowish color, close your eyes, close the lid and back away... that's chlorine gas.

    I was once told that in California, pool guys would drive around with a pressurized tank of chlorine gas in the back of their truck. They would pull up to a pool, reel out a hose with a wand attached, stick the wand in the pool water, and give the pool a shot of pure chlorine gas. I've never confirmed this with my own eyes, so I can't say it's true, but I wouldn't be surprised.  But it sounds potentially dangerous to me, and I've certainly never seen anyone in Memphis performing such a procedure. 

    Instead, chlorine is typically processed and combined with other materials to make it safer, more stable, and thus easier for the consumer to use and store. Chlorine comes in three familiar forms: 1)liquid, 2)powder, and 3)tablets. We'll touch on each in turn, but no discussion of chlorine types should begin without mentioning this: mixing different types of chlorine together can cause fire and explosion. Don't believe me? Then click here. It's also important to read the labels on your pool chemical containers. They have a lot of good information about safety, first aid, contents, application methods, dosages, storage, and much more.

 1) Liquid chlorine can be purchased in five gallon drums from pool supply companies or in plastic one gallon (or smaller) jugs at the drug store or supermarket. I honestly don't know if the two have the same strength or if ordinary bleach is diluted. In front of me I have a gallon bottle of Ultra Clorox bleach (with fresh wildflowers scent). It's official name is Sodium Hypochlorite, meaning it is salt based. I haven't tested the pH but I'm assuming it's probably neutral(?). It has no sunscreen added, so it will dissipate rapidly on a sunny day. It can be used either as a shock treatment or as a daily disinfectant.

    I'll take the cap off and carefully sniff it... Yeah, I guess it does smell a little like wildflowers, but it still stings my nose and makes my eyes water a bit. This can be poured directly into a pool, spa or fountain for quick dispersal. If you want to see something cool, put a little bleach in a cup and then add a drop of chlorine test solution (OTO) to it. 

    2a) Powdered chlorine comes in three flavors. The most common is Calcium Hypochlorite (often called Cal-Hypo) meaning it is calcium based. It has 65% available chlorine, while the remaining 35% is calcium. In fact, fully one third of the powder will settle to the bottom of the pool as white calcium. Calcium will cloud the water, at least temporarily until it's filtered out, and since it has a high pH it drags the pH of the water up. This is sometimes desirable and sometimes not. Also, it contains no stabilizer (i.e., sunscreen) so the high chlorine reading you get from shocking the pool with this type of chlorine doesn't last long. Cal-Hypo is designed to go quickly into the water, then dissipate quickly so you can swim the next day. Because of the calcium residue, this type of chlorine is not often used as a daily disinfectant, but rather as a periodic shock treatment. 

    2b) A second type of powder is called Sodium Dichlor, which is simply referred to as Dichlor. It is a salt based chlorine, has a fairly neutral pH, and contains anywhere from 56% to 62% available chlorine. The salt dissolves quickly in the water so it doesn't produce a cloud. But it doesn't seem to have the same shock punch that calcium hypo has. Also, dichlor has a sunscreen added (cyanuric acid) which makes the chlorine molecule last much longer. Thus if you shocked your pool with this type of powder, the chlorine level would stay high for a week and you wouldn't get to swim. So this chlorine is suitable as a regular additive to maintain residual chlorine levels, and it is particularly useful when winterizing and covering a pool.

    2c) A third type of powdered chlorine is Lithium based. To be honest, I need to do some research before I say anything. I've only used it once when a customer provided it, and that was three years ago. So let me take this question and come back to it at a later time.

    We've talked about liquid and powdered chlorine. Now let's discuss tablets. They come in two basic types: Trichlor and Cal-Hypo.

    3a) The most widely-used tablet is called Trichloro-S-triazinetrione, which we affectionately call Trichlor for short. This chlorine is the strongest of all the types (except pure gas) with 90% available chlorine, and since it has a sunscreen it lasts a long time too. It has a rather low (acidic) pH, which helps offset the high pH of a plaster pool; but it can drive the pH of  a vinyl or fiberglass pool too low (baking soda counteracts this).

    Trichlor comes in several sizes and shapes: 1 inch round tablets, 3 inch round pucks, cylindrical skimmer sticks, to name a few. It works quite well for everyday chlorine use because it can be dispensed in an automatic chlorinator, added to the skimmer basket where it dissolves, or placed in a floating chlorinator directly in the pool. In a pinch I have been known to crush tablets into powder for a super long lasting shock treatment (great for dark green pools), though I don't recommend this for novices.

3b) Calcium Hypochlorite (Cal-Hypo) now comes in a tablet form, though most of us know it as powdered shock treatment. They are smaller than Trichlor tablets, they have rounded edges, and they have a slightly greenish tint (unlike Trichlor tabs which are bright white). One marketing practice for Cal-Hypo is for manufacturers to wrap a compressed stick in plastic so that it can be dissolved in a skimmer. 

    New pool owners have to be careful not to accidentally mix these with the Trichlor tablets. Just like with powdered Cal-Hypo, mixing the two types of chlorine together can cause fire or explosion. (See Lesson 2 - Safety First for anecdotes about mixing different types of chlorine.) Cal-Hypo tablets are generally cheaper than Trichlor, and there's nothing wrong with using them, just remember that the two types are not interchangeable.

    I've covered most of the basics of using chlorine to disinfect your pool, but there are three other products that work with chlorine that I want to mention. They are 1)Stabilizer, 2)Oxidizer, and 3)Algaecide.

    1) You've heard me mention sunscreen above. Liquid chlorine and Cal-Hypo do not have sunscreen, while Dichlor and Trichlor do. Stabilizer and Conditioner are the common names for sunscreen; the proper chemical name is Cyanuric Acid. I like the word sunscreen because it describes what it does: it makes chlorine last longer by shielding the chlorine molecule the Sun's ultra-violet radiation (you know, that stuff that causes sunburns). We could call it Sun-blocker, or as one pool guy named Bryant likes to say, "Sunglasses for pools".

    Stabilizer can be in the chlorine, but it can also be added to the pool through the skimmer in the form of coarse white granules. If you don't have a stabilizer test kit, then take a water sample to the pool store or have your pool professional come out and test it. If it's too low, say 25 ppm, a few pounds can be added to boost the reading to 50 ppm. A reading of 100 ppm is considered to high and can be diluted by draining some of the pool water then refilling with fresh water. (Again, it is a good idea to test the fill water to know it's chemical balance.)

    Experts recommend checking the stabilizer level when the pool is opened in the spring, again as summer starts to heat up, and prior to closing the pool in the fall. If you use Trichlor tablets, then you are already adding cyanuric acid to the water, and may not need to supplement with stabilizer. 

    If you do have to add stabilizer, the instructions will likely say to pour it slowly down the skimmer. They are not kidding. Slow is the key, or else you may clog your pump basket. This product is designed to accumulate on top of the sand in a sand filter (or in the creases of a cartridge filter, or on the louvers of a D.E. filter) and it will slowly dissolve over several hours. 

    2) Oxidizer has a proper name, but we never call it that. What it does is kind of interesting. It shocks the pool without adding chlorine. Another way to put it is that oxidizer freshens up whatever chlorine you may have in your pool. 

    Oxidizer is a product that when added to the water, helps to start the chemical reaction that converts bound chlorine into free chlorine. Sometimes you don't want to add a big dose of chlorine to your pool. Maybe you've got guests coming over in a few hours and you just want to freshen up the chlorine already in the pool. That's what oxidizer does. Note that because oxidizer only works on chlorine, if you add it to a pool with no chlorine then you'll get no results, and your money is wasted.

    But if a pool has chlorine in it already, then oxidizer will burn off the bound chlorine leaving just the free chlorine swimming around waiting to go to work. Another nice thing is that you don't have to add a certain minimum threshold amount to get an effect. If you add one pound it oxidizes a little, if you add four pounds it oxidizes four times more. Plus you can swim immediately after it disperses in the pool, and it doesn't cloud the water. Add to all this the fact that oxidizer is not very costly, now we're approaching the niftiness of sliced bread.

    3) Algaecide can refer to any chemical that kills algae, so by that broad definition chlorine is an algaecide. In fact chlorine by itself does a pretty good job killing algae. But here I want to talk about products that are designed specifically to kill algae (sometimes a specific kind of algae) and which are often used to augment chlorine. 

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