Surface Water Draw-Off System
Most of the pollution in a swimming pool will sit in the top 150mm of pool depth. Therefore, there needs to be an effective system for removing as much of this pollution as possible. There are three different types of surface water removal system:
- Scum trough
Which system is installed on a pool is largely down to when the pool was built. Deck-level systems are the newest type, scum trough systems are the oldest. Each system has varying degrees of effectiveness at removing surface water pollution. How much pollution is removed is dependent on how much water exits the pool at the surface. With the scum trough and skimmer systems, 20% of the water leaving the pool to be circulated around the system is leaving at the surface, with the other 80% leaving at the floor outlet grills, which are usually located at the bottom of the deep end in a typical swimming pool. With the deck-level system, the situation is vice-versa, with 80% of the water leaving at the surface, with 20% leaving at the floor outlet grills. This makes the deck-level system the best of the three at removing surface water pollution.
The surface of the pool water is level with the deck of the pool, with water constantly overflowing into a drainage channel which goes around the perimeter of the pool. This is a very effective system for removing pollution on the surface of the water. With this system, 80% of the pool water leaving the pool is leaving via the surface and 20% is leaving via the outlet sumps.
The pool water that overflows into the drainage channel drains into a balance tank, then onwards to the plant room and then back to the pool.
The pool deck is laid to falls, which means that the floor slopes downwards slightly towards the drainage channel to allow water to drain away on its own
This system involves several skimmer baskets built in to the pool deck. Water enters the baskets through rectangular opening in the pool water. The baskets trap the larger particles of surface pollution and have to be removed for cleaning on a regular basis.
With this system, the pool water overflows into a trough that is built in to the pool wall. Providing that the pool water level is at just the right place, the water will overflow as intended, thus removing the surface water pollution. If however, the pool water level is too high, or too low, the water will not overflow and instead will lap against the sides of the pool, forming a scum line over time. As well as looking very unsightly, this scum line will harbour bacteria as a biofilm will gradually start to build up. This biofilm will serve to protect any bacteria against the disinfectant in the pool water and also be a source of nutrition.
Quickly Remove Excess Physical Pollution on Pool Surface
Excess physical pollution floating on the surface of the swimming pool can sometimes cause a problem for pool plant operators. The heavier physical pollution sinks to the bottom, but the lighter stuff remains floating around on the surface and looks extremely off-putting to pool users. This type pollution usually consists of things like; bits of float, plasters, hair etc. There will also be chemical pollution sitting on or around the surface of the pool, consisting of such elements as biofilm, grease, sweat, mucus etc.
Modern pools are usually deck-level, meaning that the surface of the swimming pool is level with the deck of the pool surround. This system is very good at removing much of this pollution that resides on the surface, and within the top 150mm. because as the water laps over the edge of the pool, the pollution enters the drainage channel that goes around the perimeter of the pool.
In older pools, the deck-level system is not so common and instead, there may be a skimmer system or a scum trough channel. The skimmer system is not very good at removing pollution from the surface as the skimmers do not go around the entire perimeter of the pool like a deck-level drainage channel does, so not nearly enough surface water goes through the skimmer for this to be an effective system. The scum trough channel system isn't any better because if the pool level is too high or too low, the swimming pool water will not flow over the channel in the correct way and you'll end up with what is known as a 'scum-line', which needs to be regularly scrubbed off manually.
If you've got either of the older systems (scum trough or skimmer), chances are that at some point you've experienced going on to poolside and seeing excess debris floating around on the surface with a public swim session about to commence in a few minutes. There is a quick and easy technique that you could use to quickly and easily bring the swimming pool back to a reasonable standard of appearance in order bring the appearance of the swimming pool back to an acceptable standard. You'll need two people, a rope that is as long as the width of the pool and a few towels.
- Drape the towels over the length of the rope while it's lying on the poolside.
- Get one person on each side of the pool and slowly drag the rope down the length of the pool, from shallow to deep.
- What you should see is the towels acting as a filter/barrier. It will catch some of the smaller particles in the material of the towels, while at the same time push some of the larger particles towards the deep end outlets. You will probably also need to get the nets out and spend a few minutes going over the pool surface and collecting any debris that remains.
- After you've completed this process, which should only take a matter of minutes, you should see that the appearance of the swimming pool has been greatly improved.
It should be stressed that this technique is a 'quick fix' only in order to get you out of trouble when you're under pressure. If any of the pool water test results are outside the correct parameters, then the appropriate action should be taken. But if all test results are satisfactory, then this method should come in handy. If you're experiencing this problem regularly, it is an indication that there is an underlying problem somewhere. The pool plant operator should ask the following questions:
- Are swimmers taking pre-swim showers?
- Is the bathing load too high?
- Is the correct circulation rate being achieved?
- Is there enough fresh water going in (30 litres, per bather, per day)?
- Are backwashes being carried out frequently enough?
- Are the skimmer baskets being cleaned out frequently enough?
- Are you using a coagulant, and are you dosing it correctly?
- Is the skimmer valve closed, or being throttled back for any reason?