8.1 Introduction

_ Improved filtration and reduced backwashing of filters
_ Elimination of bacteria
_ Improved effectiveness of chlorine
_ Amount of chlorine needed is reduced
_ Reduction of \swimming pool smell"
_ Protection against limescale (may require additional HydroFlow unit)

8.2 Background on swimming pools

Swimming pools can vary in size from domestic spas to Olympic sized pools, but they all have some features in common, and therefore all suffer from similar problems that we can address with Hydropath Technology. All pools will collect dirt and debris in the water over time, and so will need to have this removed by a filter. All pools will also need some method of combating bacteria and algae that would otherwise grow. The usual treatment is to add chlorine to the water, which acts as a disinfectant.
Unfortunately, chlorine can combine with organic chemicals such as urea
Figure 8.1: An Olympic-sized pool treated with Hydropath technology.

(found in sweat and... other substances) to become fixed chlorine" (chloramines) which is a less effective disinfectant and also causes the swimming pool smell. If the pool water is heated, then as is the case whenever water is heated, limescale can form.
In a test on a pool in Fyrishov, Uppsala you could see 80% reduction of chloramines.
8.3 Benefits of Hydropath Technology in Swimming Pools

8.3.1 Improved Filtration

Hydropath technology improves filtration, and reduces the frequency and duration of filter backwashing by around a factor of three or more. For a more detailed discussion, see section 6.
Filters remove small suspended particles from the water. The most basic idea is that they act like a sieve, allowing the water to pass through but picking out the particles. One of the most common types is a “sand filter" where water is passed through fine-grained sand. The particles get stuck in
the sand and the water passes through. The smaller the particle, the harder it is for the filter to remove it. Hydropath Technology works by applying an electric charge to the small particles so that they stick together to form larger clumps (this is called occulation). These larger clumps are then more easily removed by the filter. Furthermore, the large clumps do not penetrate so far into the filter

            a)                                    b)
Figure 8.2: Hydropath technology enhances filtration (a) and eliminates bacteria (b).

and the filter is easier to clean - see figure 8.2a. Some domestic pools will use a chemical such as alum to perform this job. Not only is Hydropath technology able to flocculate without the cost of chemicals, but the flock formed is stronger and longer lived than chemically formed flock.
Backwashing is the process where the particles that have collected in the filter are removed, cleaning the filter. This is done by forcing water back through the filter in the opposite direction to the usual water flow (hence “backwashing", see figure
6.3). The dirty water containing the particles is
then discharged. Up to 10% of the pool water can be used in each backwashing. The user will have to pay for the cost of disposing this water, the cost of water to replace it and the cost of heating this replacement water. Because the particles are larger and are not embedded in the filter, the
duration of the backwashing can be reduced and less water is used. Using less water means a lower metered water cost, lower effluent charges and reduced costs associated with heating the new water. Another advantage is that the enhancement of filtration allows smaller suspended particles to be removed that could not otherwise. This leads to much better looking, “crystal clear" water.

8.3.2 Elimination of Bacteria and Algae

Hydropath Technology kills Bacteria and Algae without the use of chemical disinfectants, making pools safer and more pleasurable. For more details see section 5. The bacteria (and algae) are killed in what is perhaps a surprising way - by using pure water. If a bacteria is dropped into distilled water that contains no salt at all, then water is forced into the bacteria from outside. This is due to the process called osmosis whereby water will move from a region of low salt concentration (outside the bacteria) to a region of high salt concentration (inside the bacteria). This causes the bacteria to swell and eventually burst. Hydropath exploits this effect to kill the bacteria in pool water.
The Hydropath signal causes the bacteria to become electrically charged when they pass through the ferrite ring. The bacteria then attract a layer of extremely pure water, containing no salt at all. The water from this layer then is forced into the bacteria due to osmosis, and the bacteria are killed
(see section
5.4 and figure 5.3 for full details).
Hydropath technology improves the safety of the water and eliminates/ reduces the unsightly green scum that can form on the surface of the pool. The amount of chemical disinfectant can also be greatly reduced, leading to substantial savings.

8.3.3 Reduction of chlorine use and the swimming pool smell

Chlorine is used as a disinfectant to kill bacteria and algae in the pool. However, its effectiveness is reduced when it combines with various organic substances (e.g. from sweat and urine). When combined with these it forms chemicals called chloramines and is sometimes referred to as “fixed chlorine." These chloramines are less effective as a disinfectant. The free chlorine is continually being converted to fixed chlorine, so more and more chlorine needs to be added to the pool.
In addition, the characteristic smell of swimming pools, sometimes called the “chlorine smell," is in fact not due to the chlorine itself but rather to the chloramines. It is also the chloramines that cause the painful “red eye" effect. Therefore, if we can break the chloramines (fixed chlorine) back into free chlorine, it will be a stronger disinfectant and have a weaker smell. One method of breaking down chloramines is to add a large amount of extra chlorine into the water in a short period. This is known as “shock treatment" and obviously increases the amount of chlorine needed, adding to the costs.
The Hydropath signal applies an electric field to the chloramine molecules, pulling them apart and thereby releasing the chlorine (fig.
8.3). Additionally, because the Hydropath signal removes organic materials via improved filtration, there are fewer organic molecules to form chloramines in the first place. Hydropath Technology therefore eliminates the need for chlorine shock treatment, reduces the amount of chlorine that needs to be added to the pool, and reduces the “swimming pool smell" that comes from the chloramines. Additional an 80% reduction of trihalomethans is seen.
Figure 8.3: The Hydropath signal breaks down fixed chlorine (choramines) into
free chlorine.

8.3.4 Protection against limescale

Limescale occurs when the minerals dissolved in water get deposited on the surfaces of heaters, pipes and other equipment as a hard mass (for more details see section 3). When deposited on heaters it can reduce their effectiveness and cause damage. It can also block pipes and valves, reducing water flow and impeding the valves' function. Removing limescale is a time consuming and expensive process, often involving acid treatment. Hydropath technology prevents limescale without the use of chemicals by encouraging the minerals to form into tiny crystals in the water, rather than form deposits on the surface of the pipe. These tiny crystals are washed away by the water flow, and removed by the filter. By preventing limescale, Hydropath technology improves the eciency of heaters, eliminates the need for them to be descaled, and increases their lifetime. Effective treatment of limescale may require a separate second HydroFLOW unit.

8.4 Water pH and its control
One thing that needs to be regulated in pool water is the acidity/ alkalinity level, or the pH. The pH measures how alkaline the water is, i.e. a low pH is Acid, a high pH is alkaline. Neutral water is pH 7. The pH level is an important part of pool maintenance and so it is worth having some background knowledge.
Roughly speaking, water with a low pH (acid) will be corrosive, whereas high pH (alkaline) will be scale forming, so the balance of the water needs to be carefully maintained. Generally speaking, pool water should be roughly kept around 7.0 - 7.6 pH.
High pH - Alkaline (hard) water has a tendency to accelerate the precipitation of minerals out of solution and form scale deposits. High alkalinity is controlled by adding acid to the water. Since Hydropath technology prevents problematic scaling, the pool can be run on alkaline water and the
usage of acid can be greatly reduced.
Low pH - Acidic water has a tendency to dissolve the pool's marbelite or plaster surfaces, creating a roughness which is ideal for algae growth. A similar result occurs in the grouting of tiled swimming pools. Low pH is controlled by adding hardness also known as "alkali" to the water.
Many pool owners find that maintaining pH at a constant level is a tricky problem. If the incoming water is acid, the pool water will keep returning to acid, if the make up water is alkaline, the pool will return to alkaline. In pools where the water is too alkaline, then Hydropath technology will help stabilise the pH. As more and more alkaline water is added, the water will eventually become supersaturated and at this point the ions will begin to precipitate out. This means that the Hydropath unit will prevent the water from becoming any more alkaline,
i.e. it will stabilise the pH. However, if
the water is too acid, then Hydropath doesn't directly effect the pH in this way because the water never reaches super-saturation.
One benefit that occurs for both acid and alkaline pools is that with Hydropath the quality of water is improved (less water needs to be exchanged to maintain water quality) and the amount of backwash is reduced. This means that less of the alkaline (or acidic) make up water needs to be added, so the pool will take longer to revert back to its original alkaline (or acidic) state. In this way using Hydropath will help stabilise the pH level in pools using both acidic and alkaline make-up water.

8.5 Results

8.5.1 Testing the water for chlorine

Both domestic and commercial pool users test the water for the level of chlorine present. This will usually be the level of free chlorine but may include the level of fixed chlorine as well. It is the free chlorine that is important as free chlorine is most effective at killing bacteria. When the pool user finds that the level of free chlorine drops too low, they add more chlorine to the water. After fitting a Hydropath unit, the user should find that less chlorine needs to be added to the water, as the unit prevents the chlorine becoming fixed. A smaller amount of chlorine will need to be added to maintain the same level of free chlorine.
If the user is also measuring the fixed chlorine (chloramine) level, they will test to see if the ratio between fixed and free chlorine becomes too high. A high level indicates that lots of the chlorine is becoming fixed. In this case, the user will \shock dose" the pool with a larger amount of chlorine,
which frees up the chlorine that has become fixed. A Hydropath unit will reduce the frequency that this shock treatment is required.
In larger pools with an automatic dosing system, the testing is done automatically, but the user will see that the frequency of dosing is reduced. It is worth double checking that the customer is indeed measuring the free rather than fixed chlorine otherwise no difference will be seen. Similarly, it may be worth checking that the automatic dosing system is measuring free rather than fixed chlorine - or even if it is simply set to dose the pool at set intervals, in which case they will obviously see no change in the amount of chlorine used!

8.5.2 Water Clarity

The user should notice enhanced clarity of the water as the small suspended particles get removed. This can sometimes be seen in a particularly dramatic manner if the user has an underwater light - the light will no longer show a \beam effect" indicating that the water has become clearer.

8.5.3 Cost Savings

The cost savings associated with Hydropath Technology begin immediately. The signal prevents chlorine from being converted to chloramines, so less new chlorine needs to be added. Within 30 minutes, automatic dosing systems will need to add less new chlorine to keep the chlorine at acceptable levels.
Figure 8.4: A spreadsheet is available from Hydropath to calculate a detailed breakdown of pool costs and savings.

The amount of new chlorine added can be reduced by as much as 66%. If the testing and chlorine dosing is done manually, the user should be able to observe a similar effect. The major savings come from the reduction in the frequency and duration of backwashing. Within one week the duration of backwashing can be reduced by as much as a factor of five, and the time between each backwashing can be extended by a factor of three. This saves money on sewage costs, the cost of new water to replace that used in backwashing, and the cost of heating the new water. The customer may find initially that more backwashing is required, as the filter begins to remove finer particles that it could not previously remove. Once the water has been cleared, the amount of backwashing required should reduce over time.
Hydropath technology can lead to significant saving for a pool of any size, from a small private pool to an Olympic size pool. A spreadsheet is available to give a detailed calculation of cost savings for a particular pool (fig.

8.6 Positioning of the Unit

Correct positioning of the unit is vital for the most effective water treatment. Hydropath enhances filtering by charging small particles so that they flocculate (clump together) into larger clumps. For the best effect, we require 1) that the particles spend as long as possible after being charged before they get to the filter so there is longer for them to clump and 2) that the water is "mixed up" through turbulence so that the oppositely charged particles come into contact and clump (see figure 6.6)
                   ^pump             ^filter               ^Hydropath unit

Figure 8.5: For maximum enhancement of flocculation and treatment of bacteria, the unit should be fitted on the inlet to the pumps, as far back as possible.

For these reasons, the unit should be fitted on the inlet to the pump, as far before the pump as possible, as in figure 8.5. This is the best location for both improvement of filtering and the breakup of chloramines. If it is not possible to fit the unit before the pump, it can be fitted between the pump and filter with a reduced effectiveness. The effectiveness may also be
reduced when the pipe systems are larger than 200mm due to the reduced turbulence in the system.
The bacteria are charged and then killed whenever they pass through the HydroPath unit. Thus the water is being treated for bacteria only as it is pumped past the unit.
If protection against limescale (section
3) is desired, an additional HydroFLOW unit should be fitted before the heater. Passing through the pump and filter will degrade the clusters, and the signal might struggle to pass through the filter, so this is why we suggest fitting a separate unit if limescale treatment is a requirement. In the case of unheated pools, the water is being heated by the sunshine within the pool itself so the the HydroFLOW unit should be fitted just before the water is returned to the pool (i.e. after both the pump and filter).

8.7 Frequently Asked Questions

Q: The unit was working, but then it rained and the pool became green. What happened?
A: After heavy rains, a lot of material can get washed into an open-air pool, adding a large amount of algae to the pool. This has not been passed through the unit and so has not been killed. As the water is pumped past he unit, it will be killed, so the pool may clear up over time. However, if there is a large amount of algae in the pool, it may be growing faster than the pump can pump the algae through the unit! In this case, it may be necessary to shock treat the pool with chlorine.
Kontakt: CMI AB   018-262660