Chemicals
It is important that all pool owners understand the role of the various chemicals used to keep pools clean. Basically, if the water in the pool is clear and blue, the following three conditions should be satisfied:
- The acidity-alkalinity balance is correct,
- All algae and bacteria have been eliminated, and
- All suspended solids have been removed.
The object of treating the pool water is to maintain these balances. If any of them is allowed to get out of control then the water in the pool will not be sparkling blue.
Using a test kit
The test kit has two vials for testing both the pH and the chlorine.
- Rinse the test vial and fill to the mark with water.
- Add 5 drops of phenol red solution for pH test in the pH vial and OTO for chlorine test in the chlorine vial.
- Place the caps on the vials and invert several times
- Compare the reading with the colour chart on the test kit.
The ideal pH for pool water is between 7.2-7.6 whilst the ideal levels for chlorine should be between 1.0-1.5.
1. Acidity-Alkalinity (pH)
The balance between the acid and the alkalines in a pool is measured on the pH scale, which can vary between 1 and 14. Distilled water has a pH of 7.0 (neutral) and the ideal pH for pool water is between 7.2 and 7.6. If it is allowed to go higher than this (too alkaline) the water may become cloudy and the effectiveness of chlorine to kill bacteria and algae will be reduced. If the pH drops below 7.0 (too acid) then steel fittings will start to corrode and the water will irritate swimmers' eyes. The effectiveness of chlorine will also be diminished. PH can be easily measured using a test kit, which has a colour-coded comparator for easy reading. When a pool is first filled the pH should be tested daily until a consistent reading is obtained. There after testing need only be done once a week or even less frequently if the water remains clear and blue.
2. pH too high (above 7.6)
If the pH is too high it must be lowered by the addition of acid. The acid can either be in liquid or granular form, " pH MINUS" being liquid hydrochloric acid.
The dosage rate to reduce the pH is approximately 60 cc (gms) of acid for each 0.1 reduction in pH for each 10,000 litres (10m3) of water. The quantity of acid (in cc) to be added for various sizes of pool can be calculated using the table below:
After adding acid the water should be allowed to circulate for four hours before testing again. If the pH is still too high then the procedure outlined above should be repeated.
3. pH too low (below 7.2)
If the pH is too low it can be raised by using "pH PLUS" which is a powder form of soda ash (sodium carbonate). The procedure is the same as outlined above for reducing the pH but the dosage rate is 50 gms per 0.1 increase in pH per 10,000 litres. The table below gives the quantity of "pH PLUS" (in gms) to be added to various sizes of pools.
As "pH PLUS " is a powder it is best to pre-mix it with water before pouring the concentrated solution into the pool.
The checking and re-application procedure is as for pH minus.
4. Sanitation and Removal of Algae and Bacteria
This section deals with disinfecting the pool water to keep it free from harmful bacteria and algae. If algae are present in large enough quantities the pool water will turn green and one of the methods outlined below can be used to make sure that this does not happen. Algae can also manifest itself as a black growth between the tiles or in crevices in the pool wall or floor.
5. Chlorination
By far the most common treatment to kill algae and bacteria is to add chlorine, which is a powerful oxidizing agent. It can be obtained in many forms including gas, liquid, powder, granules and tablet. For safe and effective disinfection regular dosing is necessary so that there is a residual chlorine level of 1.0 part per million (ppm). This is normally achieved by adding 1.5 to 3.0 ppm of available chlorine, the most effective time for treatment being in the evening as chlorine is oxidized by sunlight.
The weight of chlorine to add will depend on the quantity of free chlorine in the various products available a summary of which are given below:
CHLORINE "65": Also known as Calcium Hypochlorite, chlorine "65" is a granular form of chlorine and as the amount of available chlorine is 65%, the daily dosage rate is 25 gms for every 10,000 litres if the water is clear rising to between 75 and 150 gms for 'shock' treatment. Chlorine 65 is basic and should be added when the pH is 7.2 and below.
CHLORINE "90": This is a powder form of chlorine with 90% available chlorine. The base is trichloro-isocyanuric acid and its use has the added benefit of reducing the chlorine loss from sunlight. The daily dosage rate can thus be reduced to 15 gms for every 10,000 litres when the water is clear and blue rising to 100 gms for shock treatment. CHLORINE "90" is often recommended as it helps to stabilize the water.
Chlorine 90 is acidic and should be added when the water pH is 7.6 and above.
Under normal operating conditions chlorine dosing will be sufficient to kill any algae in the pool water but if certain types of algae do become established, an algaecide must be used.
Pool & Spa EA markets two algaecides: "ALGAE TOUCH" and "ALGICURE".
"Algae Touch" is an organic algaecide, which can also be used to improve the clarity of the water. The dosage rate is 200ccs (gms) per 10m3 (10,000 litres) and a single dose is normally sufficient to kill all the algae in the pool. However, if growth is still apparent after three days, the dosage should be repeated.
"Algicure" is a copper-based algaecide. After dosing with 400 cc (gms) per 10m3 (10,000 litres), the pool water should be circulated for 24 hours. The algae can then be removed by using a stiff brush. If necessary, the treatment can be repeated to remove particularly stubborn algae.
7. Removal of Dirt
Occasionally it may be necessary to remove solids suspended in the water (rather than dissolved in it). This normally occurs when the pool is first filled-especially if borehole water is used.
As larger size dirt particles quickly settle to the bottom of the pool where they can be removed by vacuuming or brushing, they do not present a problem. But as the particle size decreases the settlement time gradually increases and the smallest size particles remain permanently in suspension. In order to remove these particles, the water must be dosed with “FLOCULANT". The flocculant sticks to the soil particles thus effectively increasing their size and weight. They then settle to the bottom of the pool (a process called flocculation) where they can be removed by normal filtration or vacuuming.
The quantity of "FLOCULANT" to be added will depend on the amount of dirt in the pool but initial dose of 50 ppm is normally recommended. This works out at 500grams for every 10 m3 (10,000 litres) of water.
Flocculant is supplied in granular form so it must first be premixed to form a concentrated solution before it is added to the pool. The concentrated solution should be poured around the edge of the pool and the pump should be kept running for three to four hours to make sure that it is mixed effectively. Alternatively, the flocculant can be placed in the line strainer on the pump where it will gradually dissolve while the pump is working. The pump should then be switched off and the particles allowed to settle preferably overnight. Any sediment dirt can be removed by filtration. This can sometimes take two to three days if the water is particularly dirty or if there are a large proportion of clay sized particles.
8. Anti-Stain
"STAIN REMOVER" is a detergent specially formulated for use in swimming pools. It is effective in the removal of scum from the top tile layer as well as for cleaning handrails and other exposed pool accessories. It is normally applied by cloth but where the staining is excessive a scouring pad can be used.