Water Balance is the other half of Pool Chemistry. Unfortunately, it’s the half that is often ignored.
You can tell when water is balanced as it has that very attractive sparkle about it.
There are three major chemical levels in water balance,
Of these three components pH will change rapidly without constant adjustment; alkalinity will change a little less rapidly than pH while calcium hardness, once set, will stay reasonably stable over time especially if top-up water has calcium hardness. For example, in Brisbane calcium hardness in tap water is about 60 ppm. Combined with water loss from backwashing the calcium hardness remains stable once set.
Temperature, cyanuric acid, and TDS levels will also contribute to water balance.
In nature, bodies of water naturally seek water balance. It could be a swamp, but it will still seek water balance.
So how does nature do that? In nature we are not throwing chemicals into water to achieve a body of water that we can swim in. Lakes, dams, and rivers are constantly receiving acid and carbonates via streams running into these water bodies. Chemical levels remain pretty well constant, and they need to for life to survive.
So, what happens when the water body isn’t balanced? The chemical level that responds is calcium hardness. The water body will either seek out calcium or choose to get rid of it.
So why should we worry about it in a swimming pool, other than the pool looking lousy? Well, two reasons,
Calcium scaling starts with the pool getting that dull, cloudy look which occurs when calcium starts dropping out of the water. This adds to the turbidity which you do not want in a pool. The next step is the calcium dropping out onto the pool surface giving it a dull look. Other chemicals can be picked up which results in a dirty appearance. As the situation get worse, calcium crystals start forming on the walls and elsewhere. These can be quite sharp.
When you get this problem, you are left with either,
There are chemicals which prevent the calcium dropping out of the water. These chemicals should not be used with a chemical controller as they affect the probes. They shouldn't be needed if the pool is properly maintained.
Calcium corrosion is the opposite to calcium scaling. This occurs when the calcium hardness is a body of water is too low. The water starts looking for the calcium in everything with the most obvious targets being the pool wall if concrete, tile grouting and pool finishes. This doesn’t happen overnight, but it does happen. Eventually you will be up for expensive repairs which can include,
All avoidable, or at the very least, the risk greatly reduced.
We use what is referred to as the Langelier Saturation Index (LSI).
It’s a formula which gives us a number which we want to keep between plus or minus 0.5 as much as possible.
There are many LSI calculators on the internet. You can use one or more of these to establish the calcium hardness level you want in your pool.
Once you have decided on the pH level, the alkalinity range and cyanuric acid (if you use it at all) levels that you want to operate a pool at, then you can use those levels with the pool temperature and TDS level to work out what your calcium hardness level should be.
Enter the figures into your chosen calculator then enter various calcium hardness levels until you get an achievable LSI range that you can keep between -0.5 and + 0.5. Now you can add calcium chloride until you get to your desired level. You need to be careful with this one. Overdo it and you will be in trouble as you will have to dump water to get rid of it.
Once you have worked this out it interesting to play with the figures, especially pH and alkalinity, to see what effect there is on the LSI. I did this years ago using the chemical level ranges you commonly see recommended. I found that if you kept your chemical levels within those ranges then your LSI was ok. Knowing that, meant that I didn’t have to waste time on working it out except for maybe occasionally to check something.
Professor Langelier came up with a formula that ended up being called the Langelier Saturation Index while researching water scaling and corrosion in metal water pipes. It seems to me that most of what we do in swimming pools is a result of research in other areas of science. A lot of what I have learnt has been thanks to the research that has been done in environmental studies. There is plenty to learn there. The Langelier story is described in the follow link.
https://blogs.illinois.edu/view/7859/915251002
I found the following web site which shows the chemistry calculations involved.
www.gov.nl.ca/ecc/files/waterres-quality-drinkingwater-pdf-calculation-langelier-index.pdf
I’ll stick to using a calculator, thanks!
