Circulation Systems

All modern pools come complete with a circulation system for keeping the pool water clean. The cycle is: pool -> pump -> filter -> pool.

As mentioned above, the most common piping layouts used to achieve this are the established "Freeboard" pool with the water level approximately 50 mm to 100 mm (2” to 4”) below the top of the pool wall and the “deck level” arrangement where the water flows over the wall into a peripheral channel at the same level as the pool surround.

The plumbing for the two systems is essentially the same with water being drawn from a main drain at the deepest part of the pool and from either a surface skimmer (for freeboard pools) or a balance tank (for deck level and horizon pools). A third suction point for a vacuum cleaner is also included on all our pools. There are thus three suction lines leading to the pump and can be controlled individually by an isolation valve.

Operating Procedure

Under normal conditions the valves from the skimmer (or balance tank if the pool is deck level of horizon) should be fully open, the main drain should be partially open and the vacuum line closed. This ensures that the water is drawn from the deepest part of the pool as well as from the surface thereby optimising circulation.

The pool circulation system should always be in operation when the pool is being used. When not in use it is normally sufficient to switch the pump on for four to six hours a day to keep the water clean. During the cold months when the pool is not in use for long periods, the operating time can be reduced. The exact pumping time is determined by the individual pool conditions.

ON DECKLEVEL AND HORIZON POOLS THE ISOLATING VALVE TO THE BALANCE TANK SHOULD BE CLOSED WHEN THE PUMP IS SWITCHED OFF.

Skimmers

Skimmers are installed on "Freeboard" pools to remove floating debris from the water surface. The effectiveness of the skimmer can be increased by slowly closing the isolating valve from the main drain while the skimmer valve is left open. The skimmer basket should be checked and cleaned every week as part of the routine maintenance of the pool. Always make sure that the floating weir (if fitted) is working properly as this has a direct effect on skimmer efficiency. If the water level in the pool is below the skimmer mouth then the skimmer valve should be closed completely to avoid the risk of the pump sucking air into the system.

Vacuum

Pool vacuum cleaners are very effective in removing dust and debris that can accumulate on the floor of the pool. The cleaner operates by sucking water through the vacuum head via a flexible floating hose to the vacuum line and thence to the pump and the filter. The floating hose should be filled with water and connected to the vacuum point in the pool wall. The vacuum valve in the plant room (which is normally closed) should then be opened and the sump and skimmer/balance tank  valves closed. The vacuum head should be moved slowly across the pool floor to avoid stirring up the dirt that has settled to the bottom of the pool. When vacuuming is complete make sure that the valves in the plant room are returned to the normal operating position.

NB: DO NOT USE THE VACUUM TO REMOVE LEAVES FROM THE BOTTOM OF THE POOL AS THEY MAY BLOCK THE VACUUM LINE. LEAVES SHOULD BE REMOVED WITH THE LEAF RAKE PROVIDED.

Filters

The filter is designed to remove suspended solids from the pool water. For domestic pools where bathing loads are light, the pump will circulate the pool water through the filter every eight hours. For pools with higher bathing loads the circulation rate is higher, typically four to six hours.

Pressure Sand Filters

These are the most commonly used filters in Kenya. Dirt and other deleterious materials are removed from the water by forcing it through the filter media, which consists of layers of carefully graded river sand. Pressure sand filters are rated according to the volume of water passing through every hour divided by the effectiveness of the filter media. Modern fiberglass filters are effective with a flow velocity of up to 50 m/hr.

Maintenance of Filters

Dirt removed by the filter will accumulate in the filter media and this eventually leads to clogging. The larger size filters have a pressure gauge on the inlet, which can be used to access whether the filter media needs cleaning. When the filter is operating effectively the operating pressure will typically be between 0.6 and 1.0 bar (10 to 15 psi). As the filter becomes blocked the pressure will rise and an increase of 0.3 bar (5 psi) indicates that it should be cleaned. This will involve backwashing and rinsing (for pressure sand and DE filters) or hosing down of elements (for cartridge filters). If no pressure gauge is supplied then the filter should be backwashed on a regular basis, normally once a week being sufficient.

Use of Multi-Port Valve (MPV)

Most modern filters are fitted with a multi-port valve (MPV) to simplify filter operation. There are six positions on the MPV and the various operations possible with the different settings are described below.

MPV Operation

Filter

This is the normal operating position. Water from the pump is fed into the top of the filter and after filtering through the media is collected at the bottom.  It is then returned to the pool through the inlet pipes.

Backwash

When the filter becomes clogged, the MPV should be turned to BACKWASH. Water will now be pumped from the pool into the bottom of the filter and out of the top.  It is then discharged to waste.  This operation normally takes two to three minutes and should be continued until the water in the sight glass on the side of the MPV is clear.

Rinse

After backwashing the filter media needs to be rinsed.  Water is pumped into the top and out of the bottom of the filter as for normal filtering but the water is then discharged to waste.  This removes any residual dirt in the media instead of pumping it back into the pool.  Rinsing should not take more than one minute and again the sight glass on the side of the valve can be used to see when the water is clear.

Recirculate

In this position the filter is by-passed completely and the water is pumped straight back into the pool.  It will normally only be necessary to use this option if there is a problem with the filter itself (e.g. a leak or a major blockage).  It can also be used if the filter is on a spa bath to increase the pressure at the hydro-jet inlets.

Waste

The waste port is used for emptying the pool.  The filter is by-passed and water is taken straight from the pool to waste.  If it becomes necessary to empty the pool make sure that the pump is not switched off once the operation has began as there may be problems with priming the pump when the water level is low.  This position can also be used for vacuuming to waste.  This may be necessary if there is a large amount of sediment on the floor of the pool, which would rapidly clog the filter in normal operation.

Closed

This shuts off all flow to the filter and the pool.  It is usually used in conjunction with the valves on the suction side of the pump to prevent water loss when it becomes necessary to remove the lid of the line strainer to clean the basket.

WARNING: WHENEVER THE POSITION OF THE MPV IS CHANGED THE PUMP MUST BE SWITCHED OFF OR THE MPV MAY BE DAMAGED.

Pumps

A typical pump for a domestic pool consists of an electric motor turning an impeller inside the pump housing. A pre-filter or line strainer is usually incorporated into the pump body. This has a small plastic strainer for collecting leaves, lint, hair etc. and prevents such deleterious material from being sucked into the pump itself. The basket can be removed for periodic cleaning by undoing the clear plastic cover on the line strainer. To clean the line strainer proceed as follows:

1. Stop the pump and isolate the suction pipes by closing the main drain, skimmer (or balance tank) and vacuum valves.
2. Turn the MPV filter valve lever to "CLOSED"
3. Open the cover, lift out the basket, clean and replace it. Carefully check the seating for the lid when it is replaced, as it must be secured tightly to eliminate air leaks.

Pumps are rated according to the power (HP or KW) of their motors; the more powerful the motor the larger the volume of water pumped in a given time. Domestic pool pumps typically vary from 0.75 HP (0.55 KW) to 1.5 HP (1.1 KW). The pump motor has a thermostat built into the motor windings, which automatically protects it from overheating. The motor itself is a brush less design and as such it does not need routine maintenance. As for the filter, the size required for a particular pool will depend on the volume of the pool and the pump must be capable of cycling the water through the filter within the desired eight hour cycle time.

Chemicals

It is important that you 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:

1. The acidity-alkalinity balance is correct,
2. All algae and bacteria have been eliminated, and
3. 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.

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.

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 granular or liquid orm and is marketed as “HIGH PH” or “pH MINUS". The dosage rates to reduce the pH will be indicated on the package.

For liquid acid approximately 60 cc (gms) of acid will be required for each 0.1 reduction in pH for each 10,000 litres (10m3) of water. 

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.

pH too low (below 7.2)

If the pH is too low it must be raised by the addition of soda ash (sodium carbonate) which is marketed as “LOW PH” or “PH PLUS”. 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. 

As soda ash 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 high pH.

Sanitation and Removal of Algae and Bacteria

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.

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.

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 gm for every 10,000 litres if the water is clear rising to between 75 and 150 gm for 'shock' treatment.

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 or 50 gms for CHLORINE "65" and CHLORINE "90" is often recommended as it helps to stabilize the water.

Salt Water Chlorinators

A method of chlorination rapidly gaining in popularity is the saltwater chlorinator. This works by generating chlorine from salt dissolved in the water. For the unit to operate, refined salt must be added to the water to raise the salinity to 4000 ppm; for a pool with a volume of 80m3 this means adding 320 kg of salt. The water will therefore taste very slightly salty (similar to the well water at the coast) but will not be sufficiently saline so as to cause red eyes (for comparison, sea water typically has a salinity of 40,000 ppm). The salt concentration should not be allowed to fall below 3000 ppm. Salt-water chlorinators have the advantage of producing chlorine on a continuous basis rather than the batch dosing needed for powder or granular chlorine.

Algaecide

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. This is marketed as "MAGIC TOUCH" or "ALGAECURE".

"MAGIC 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.

"ALGAECURE" 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.

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 flocculant which 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 500 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 is a large proportion of clay sized particles.

hth “Sparkle It”

“Sparkle It” is a recently introduced water clarifier which clears cloudy water and aids filtration. It contains liquid flocculators and should be used when the pool water is cloudy or lacks sparkle. Add up to 1 litre of sparkle It to the skimmer basket or to the line strainer and the n allow the water to circulate for 12 hours before switching the pump off and leaving – preferable overnight. The dirt deposited can then be vacuumed off the pool floor. The filter should then be backwashed.

Anti-Stain

Anti-stains are detergents specially formulated for use in swimming pools. They are 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.