A Kettle Of Fish

I wonder what the collective noun is for motorcycles. The way people ride in Bali it must be the same as for mosquitoes – a scourge of motorcycles. Bicycles? That must be a bother, a bother of bikes. Then we have a trouble of builders, a worry of architects and for a bunch of right wing politicians we have a tea party. We all know the collective noun for fish is a kettle and, of course, for crabs is a dose.

When we talk about quantities we have to wonder which of the world’s countries has the largest population? It’s an interesting question but are we talking about the number of people or the amount of people? These days a typical supersized English personbeing is getting rather large and in terms of total mass the population of Shanghai is eclipsed by the male voice choir of Upper Nether Wallop, a place noted for having more fastfood joints per stomach than anywhere else in the United Kondom.

It is estimated that if the whole population of California were to go swimming at the same time the sea level would rise by one metre and Pacific islands would vanish beneath the waves.

On the beaches in Australia they have signs on the beaches telling people that for public safety they should only swim between the flags. What they don’t tell you is that it is not for your public safety. It is, in fact, to stop a major ingress of humankind causing a tsunami that could wipe out half of the island nations of the Western Pacific. It is a clever ploy to protect their island neighbours and, as the population gets larger, they can move the flags closer together.

So what is the relevance of this? Well when a person gets into a swimming pool the water level rises, if a pod of people get into a pool it rises much more.

If the pool is an “overflow” pool (such as an infinity edge pool) the water level in the pool is kept constant so if someone gets into it they will displace water which must overflow. If the person is a rice farmer from Klungkung the amount of water displaced will be enough to fill a couple of thimbles, not much of a problem but, with “grossly obese” becoming the new norm (apologies to Norm) in the Western world, when a western person gets into a swimming pool a substantial volume of water will be forced out. All that water has to go somewhere and it must be replaced later when the person gets out.

To cope with these variations overflow pools need a buffer, a tank that can hold extra water when someone gets into the pool and then provides a reservoir of water to be pumped back in when the person gets out. This is called a balance or balancing tank.

This process of collecting overflowing water and pumping it back in is all part of a swimming pool’s circulation system. Water circulation is an important consideration for any swimming pool and achieves three things:

1. It maintains the water level as we have mentioned.
2. It cleans and filters the water. There are many things that can contaminate a swimming pool from leaves dropping off trees; dogs, rats and cats that might fall in and, of course, little boys doing what little boys do in swimming pools.
3. It treats the water to kill bugs and stop it growing green algae and other living things. If left untreated for even a few days the water is likely to turn green as algae takes a hold and multiplies.

Water overflowing from the pool is the start of the water circulation system.

Overflow Pools
In many modern private pools the water overflows over an “infinity edge” into an overflow channel. Infinity edges are popular because they allow very effective design possibilities for architects. Many older designed swimming pools (particularly public pools) have overflow channels built around the inside of the walls of the pool with the water level below the upper edge of the pool. Modern designs tend to have the overflow channels set into the paving surrounding the pool set back from the edge so the pool is full right up to the same level as the pool surround. In many private homes the water overflows along one side of the pool running into an overflow channel set along the outside of the pool wall.

In these “overflow” designs it is important that the water level is kept exactly to the level of the overflow so the water will keep overflowing. Unfortunately the amount of water in a pool varies not only as a result of people getting in and out as we have said but also as a result of water loss through evaporation and/or leaks (if there are any) all these factors are coped with by the balancing tank.

The overflow channel(s) carry the water to the balance tank which is set below pool level.
Skimmer Box Pools
Many pools are not overflow pools, the water level is below the top of the pool walls and is not constant, the level can rise and fall as the volume of water changes.

These pools usually use what is called a skimmer box. This is a small box set into the side of the pool at water level. The skimmer box feeds water from the pool directly into the pool circulation pump. Skimmer boxes allow for variations in the water level in the pool – enough to cope with daily water evaporation or large bloated human bodies. These pools need no balancing tank and so are simpler and cheaper than overflow pools.

The Circulation System
Both overflow and skimmer box pools draw water from the surface of the pool. This means there is a flow of water across the surface of the pool which carries away anything floating on the surface (hence the name “skimmer box”).

As the water runs from the overflow channels or skimmer box into the first circulation pipes it passes through a strainer basket, a coarse filter which collects large debris such as leaves, bits of wood and the odd dead body.

From here the water passes to the circulation pump which pumps the water to the second stage of filtration, which is usually a sand filter. This is a large tank full of sand and, as the water passes through the sand, any particles in the water larger than around 20 microns (that’s about the size of a mosquito’s testicle) are collected.

From the sand filter water passes on through a treatment process to kill off any bacteria and algae in the water. There are various different treatment methods to chose from the most common of which uses chlorine as a disinfectant. We’ll look at this another time.

Water is returned to the pool usually through a series of pipes set into the walls of the pool. Careful positioning is needed to make sure all the pool water gets circulated with no dead spots.

Backwash
From time to time we need to clean the sand filter and this is achieved by using extra piping and taps in the system which allow us to pump water backwards through the sand filter to release collected particles and wash them away down a drain. This processing is called backwashing. Most pools these days have fully automated backwashing systems.

One last thing we need in the circulation pipework is an arrangement to empty the pool if we need to.

Circulation Design Considerations
We need to treat all the water in the pool preferably at least once a day. Care is needed in designing a pool and its circulation system. Poorly designed pools can have stagnant areas where water can lie without being drawn into circulation, to avoid this we need careful placement of the water inlets and outlets.

The size of the circulation pump and the pipework carrying the water must be designed to carry enough water to circulate the whole volume of the pool within a reasonable time. If these are underdesigned you may have to run the pump many hours a day. If they are overdesigned you may find the circulation is costing you a lot of money.

Note that if you have a very deep pool there will be a lot more water to circulate.

Costs
“A swimming pool is a hole full of water you throw money into.”
If you have a swimming pool you will have to continuously filter and treat the water. For many people a swimming pool circulation pump is one of the larger electricity consumption items in a house and a major contributor to high electricity bills.

In addition whichever way you treat the water this will also cost money.

All this can be expensive although there are ways of keeping costs down. Before deciding to get a swimming pool it is a good idea to think through how often it will get used and how much it will cost to maintain it. Sensible design can considerably reduce the cost of initial installation and of ongoing maintenance.

Personally I have never been particularly interested in having a swimming pool, it’s not really my kettle of fish.

Phil Wilson
Opinions are those of Phil Wilson. He can be contacted through the websites at www.mrfixitbali.com or through the office on 0361 288 789.
Copyright © 2015 Phil Wilson
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