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Most commonly used pool chemicals to correct water balance

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Most commonly used pool chemicals to correct water balance | Samui Times
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Most commonly used pool chemicals to correct water balance

For water to be comfortable to swim in, it is essential that it be non-corrosive, non-scaling and correctly balanced. The various factors involved are described below. Balanced water is healthy for the swimmer and will also benefit the water proofing membrane and fittings in the pool while preventing corrosion and erosion of equipment. The recommended ranges relating to water balance are:-

pH7.2 – 7.6
Total Alkalinity :80 – 120 ppm
Calcium Hardness200 – 400 ppm
Total Dissolved Solidsless than 1500 ppm

Note – ppm is parts per million; it is the same numerically as milligrams per litre – mg/l.

To achieve a proper equilibrium in the pool water, it may be necessary to add some chemicals to the pool, and today we will have a look at the most commonly used chemicals. Sometimes pool owners ask – is this really necessary and, if so, why is this important to do? Well, the answer is actually straightforward – because it saves you money and creates a safer environment to swim in.

Previously we mentioned the importance of maintaining a correct water balance in your swimming pool and had a look at the basic parameters pertaining to this. These parameters are:

pH, Alkalinity (TA), Calcium Hardness and TDS (Total Dissolved Solids).

pH: pH is a logarithmic scale indicating whether the pool water is either acid or alkaline (basic). The scale runs from 0 -14 and neutral water (neither acid nor alkaline) has a pH 7.0. At pH values of less than 7.0, the water is acidic and may cause eye and skin irritation, metal components may corrode and pool liners may be damaged; at pH values above 7.0 the water is alkaline, chlorine becomes progressively less effective in destroying bacteria and controlling algae growth, the water may become cloudy and scale formation may occur. The ideal pH range for swimming pool water is normally between 7.2 and 7.6 for chlorine and salt water pools, and between 6.8 and 7.2 for chlorine-free pools. Sometimes the pH may be too high (most likely) or too low, but either way it needs to be adjusted to get back into the desired ranged for the specific pool.

When the pH is too high, the most commonly used chemical to lower it is Hydrochloric acid, also sometimes called Muriatic acid. The 10% solution (pH Down 10%) is the gentlest version available on Samui and is kinder to the equipment, fittings and the skin. Hydrochloric acid is also available in a 35% and 50% solution, but extreme care should be used when working with these strengths since they are much more aggressive and corrosive.

Often, when we visit a swimming pool pump-room, corrosion on the equipment – pumps and electrical boxes – as well as steel fittings and structures are very noticeable and, sometimes, downright dangerous. People often store their pool chemicals in the pump-room and this just exacerbates the situation. This is not recommended.

When the pH reading is too high – more than 7.8 – it creates a more conducive environment for the growth of algae and also has a detrimental effect on the effectiveness of the sanitizer. For example, the water in the pool will start to appear a little “darker” and rather “dull”, while the use of chlorine (if this is a chlorine pool) will be higher. The problem is that, even if more chlorine is used and at a higher cost, it tends to become less effective and may result in a more pronounced chlorine smell around the pool. It may also cause some discolouration of clothing, i.e. swimming gear or light coloured towels, or even hair.

When the pH is too low, there are essentially two chemical compounds available to increase the pH level, namely Sodium Bicarbonate (Baking Soda or Bicarb) and Soda Ash (Sodium Carbonate or Trona). Both agents achieve the same result, although slightly differently.

Total Alkalinity: Alkalinity describes the amount of alkaline compounds (carbonates, bicarbonates and hydroxides) present in the pool water. Most commonly available pool test kits do not have any means of measuring alkalinity and its importance is often underestimated. If the alkalinity is low (below 60 ppm) there can be rapid changes in pH, corrosion of exposed metals, eye irritation and even coloured water (usually green). High alkalinity (above 160 ppm) is uncommon and not so serious but can increase resistance to changes in pH, making pH adjustment difficult and may cause cloudy water.

As mentioned previously, alkalinity is closely linked to pH and provides a buffer to the pH to avoid sudden changes. We often hear of people complaining that their pool was clear and then, all of a sudden, sometimes following a rain storm or a pool party, it suddenly goes green. More often than not, this is due to the fact that the alkalinity is too low. When the alkalinity is too low, the addition of Sodium Bicarbonate is recommended to increase it without affecting the pH too much.

The desired range for alkalinity is between 80 and 120 ppm (parts per million). More often than not, alkalinity tends to be lower than the desired range. Excessive and prolonged use of chlorine – especially granular or powder – is mostly the reason for a pool with a very low alkalinity. Regular use of hydrochloric acid may also result in a pool with a low alkalinity.

Calcium Hardness: Sometimes also referred to as Total Hardness. Water is often classified as being either “soft” or “hard” and this basically refers to the mineral content in the water, of which calcium and magnesium are the most common. Calcium is also relatively easy to measure in the water. The normal range for calcium in swimming pool water is between 200 to 400 ppm. Hard water, normally with a very high calcium and/or magnesium level, may cause the water to look turbid or cloudy (milky). A common solution to the problem is to, while maintaining the sanitizer concentration at the proper level, raise the acidity (i.e. lower the pH) by the addition of hydrochloric acid, to achieve the optimum value, being in the range of 7.2 to 7.6.

TDS (Total Dissolved Solids) TDS is a measure of the combined content of all solids (inorganic and organic) contained in the water. Chemicals added to maintain sanitation, pH, alkalinity, calcium hardness and algaecide etc., all add total dissolved solids to the pool water. Dirt, dust, sun tan oils and other debris introduced into the pool by bathers also contribute to dissolved solids.

High levels of TDS and the accompanying turbidity will impair the performance of the disinfectant or sanitizer, algaecide, and other treatment chemicals added to the pool water. As TDS levels rise, more “active disinfectant” is required to eliminate organisms in the pool water. Because organisms embedded in the solid particles, causing cloudy water, are protected from the disinfectant, this is not generally a problem to TDS levels of 1500 ppm, at normal pool disinfectant levels. In addition high levels of TDS can enhance galvanic corrosion of metals, reducing the life of heaters, chlorinators, pipes and pumps. To reduce the TDS it is recommended to partially drain the pool water and replace it with fresh water.

Note: Chemicals should always, ideally, be stored in a cool and dry area.

We trust that you found this information informative and will assist you in understanding your swimming pool better. By having a well balanced pool means that you have more time to enjoy it, and maintain it cost-effectively.

Should you have any queries or require additional information regarding water testing or pool maintenance, feel free to contact Sunshine Samui Pools on 077 960 565 or

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