Efficiency depends on water treatment, filter and heater

Press, 14 July 1982, Page 18

Efficiency depends on water treatment, filter and heater

Before a spa pool is used the water must be put “in balance" - in other words, it is neither hard nor soft. In the Christchurch area, water tends to be hard and needs to be properly treated before being used in the spa pools. If the pH (Potential Hydrogen) is not within the range of human comfort, the skin is irritated.. The water in a spa differs markedly from that in a normal pool, and these differences, together with the

operating characteristics of filters, must be considered before the final selection of a filter. A filter fitted to a spa has to cope with a higher percentage of fine particles than is normally encountered in a swimming pool. Normal water contaminants are fairly evenly spread in size over the whole range. ” " Spa-, .water, on. the other hand, is an ideal growth medium for bacteria and other organic . matter. As a S result? it can be expected to

contain a much higher proportion of these fine contaminants.

The bathing load of a spa per unit volume of water is far higher than any swim ming pool, and this also contributes to the high finematter content.

For example, a spa with a capacity of more than 1800 litres (a bathing load of one person to 455 ' litres) is equivalent to 100 people in a 45,460-litre pool.

Compared to normal pool water, the introduction of contaminants per litre per hour, is very high. These contaminants are mainly body fats, oils, bacteria, mucus, hair, skin particles and normal dust and dirt.

Other factors which adversely affect the filters’ operation are chemical imbalance and the eventual tbuild-up of dissolved and fine suspended solids. These will . occur with the addition of chemicals, contaminants and top-up water. To allow the.filter to work at its peak, the spa should be drained from time to time and refilled to drop the pollutant level. The frequency of draining will depend on the use of When the spa requires , draining will be indicated by an excessively high hardness reading, unstable pH, a high total dissolved liquids level and a resultant drop in effectiveness of chlorination. The physical signs are cloudy water, excessive foaming and a rapid scum build-up at the waterline.

In general, the selection of the type of filter is a .compromise between water quality and the length of the filter cycle. Other factors include maintenance time, cost, size and the amount of water used for back-washing. The type and size of filter depends on several factor?, some of which are:

• Th? capacity of the spa. • The anticipated bathing load.'

’ • Frequency of use. • Whether the spa is for commercial or domestic use. • If it is indoor or outdoor.

• The temperature. • Whether it is linked to a main pool. Filters There are three types of pool filters available. They are a washable bag, cartridge filter and sand filter. Filtermaster New Zealand, Ltd, designs and. manufactures both the cartridge and sand filters According to Filtermaster's project engineer, Mr Geoff Church, the cartridge and bag filters are best suited to a domestic spa with a light loading. Generally, when using the bag filters, more than one bag is used at a time. The bags cost about $5 each and at least four would be needed each year, depending on the use of the spa. The cartridge filter has a life of about 12 months, depending on the use of the spa. The total cost of the complete unit is about $l2OO and a replacement cartridge costs about $7O. When cleaning is necessary, for both types of filter, they are removed and hosed down with cold water. The lower level of contaminant introduction and less frequent use of a domestic spa' mean that a cartridge system will give a long filter cycle. Because a cartridge system requires no back-wash line, there are initial savings on the unit and the plumbing requirements. ' Outside of a spa with a very light loading, these “thin” strainers are not adequate, Mr Church says. He recommends a sand filter for commercial spas and domestic spas with heavy use.

When the needle on the pump gauge moves into the black area on the gauge, it is time to back-wash the water. This is done by turning the handle on the stainless steel tank, waiting a few minutes and returning the handle to its normal position..

Sand filters have the advantage of being able to cope better with high levels of body fats, oils and live organic matter, but require a

relatively high quantity of water to back-wash. The loss of back-wash water is not a problem because of the high water volume involved. This can be an advantage because the frequent toppingup dilutes the contaminants and means less frequent water change. An automatic sand filter with a heater will cost about $1660. The plumbing requirements will also be greater, but a sand filter is still the quickest and cleanest method of filter system. The cartridge and sand filter systems can be made more efficient by pre-coating with diatomaceous earth (sedimentary rock with a highly porous lattice structure of silica). This is the finest filtering material available. Some pool specialists will not recommend DE coating for bag filters because this tends to make them block earlier. Heaters Spa pool heaters range in size from 2.5 kW to 6kW for a domestic spa. The size of the heater 'is related to the size and use of the spa. Most heaters will take between six and eight hours to heat the water to 38.5 degrees Celsius. Heating of the water above this temperature is dangerous.