As an operator, there’s always a sigh of relief when all your equipment is working as it should and all chemistry readings are within range – the water is that perfect clear crystal blue, the air is fresh, and all your patrons are happy. Of course this must mean the water is balanced, right?! It may be surprising, but this is not necessarily the case. Water balance is a measurement of whether your water is scaling, corrosive, or balanced. Water wants a certain ratio of dissolved material in it. Having the correct ratio is where the balance comes in. So how DO we measure if our water is in balance or not?
There are other ways but the most common method used in our industry for figuring out where your pool lies on the scale is the Langelier Saturation Index (LSI). The LSI looks at 5 factors (pH, Total Alk, Calcium Hardness, Temp, and TDS) and uses a mathematical equation to tell you if you are in balance or not. Just like your water chemistry has ideal operating ranges, so does LSI. Being between -.3 and +.3 on the LSI scale means your water is in balance. Being lower than -.3 means you are on the corrosive side and being higher than +.3 means you are scaling. But what do these 3 designations even mean?
Water is a universal solvent. It wants to carry around a certain amount of dissolved minerals at all times in order to be balanced. When there isn’t enough, the water becomes corrosive. Water can be very aggressive when it comes to achieving balance. It can eat away at surfaces it contacts, like the grout around your tile or the cement surface of the pool wall, causing an etching of the surface. Corrosive water can also eat away at iron and copper that is within the system, like piping, pumps, and heaters. Not only can this ruin the equipment but the dissolved metal ions in the water can now cause future staining.
On the flip side, being scaling (mineral depositing) is no better. Having too much dissolved minerals in the water will keep the water from stripping minerals from the pool surface and equipment, but it will cause the water to try and balance itself by dropping calcium carbonate out of solution. Imagine your pool as a snow globe. Not only is this unsightly, but the resulting “snowfall” can become deposited onto the pool surface, causing a very rough surface that leaves your patrons open to getting scraped up in the pool. These rough patches can also become visibly dirty looking real quick, as the rough surface will trap dirt. And this is just what you can see! Imagine what the insides of your lines or the internals of your heater look like. Cause the scale is not just collecting in places you can see. It will impact pipes and equipment much quicker than people realize, like fats in arteries.
Lastly there is balanced water. When the correct ratio of minerals is dissolved in the water, it will neither drop calcium out of solution via scale nor take minerals out of the surrounding surfaces. Having balanced water will keep your pool structure and equipment in their best condition for longer, and paired with great chemistry, will create a luxurious swimming experience in clean healthy water. And that’s something we can all appreciate!
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LSI – The Math Explanation for Pool Maintenance