Why must we disinfect the water of a swimming pool or SPA?

At places where people come together you can find big amounts of micro-organisms! Each person carries billions of micro-organisms. Swimming pools are places of sanitation but also cleanness. Taking a shower will take away many organisms but not all of them. A complete purification of people without damaging their health is not possible.

Each bather releases products in the water as urine, hair, skin particles etc.

  • These organic compounds are used by bacteria as nutrition and they will multiply extensively.
  • The infection risk depends on the disinfection doses.
  •  You can find many bacteria on the floors. In a dry environment they only can sustain but in combination with water they can multiply with the known consequences.

What’s the effect of a good water treatment?

50% of the incoming contaminants is eliminated by flocculation, filtration and back-washing. The other 50% must be eliminated by oxidizing and disinfection (=sanitizing):

Oxidizing is the process of destroying dissolved contaminants (organic debris) like ammonia, ureum, proteins, fats and amino acids which come from urine, skin, shampoos etc..

Disinfection(or sanitizing) is the process of destroying bacteria, fungi and viruses.

Which parameters must be measured in swimming pool and SPA water?

To obtain the best quality for the swimmingpool and spa water one must measure the following parameters:

  • pH
  • Chlorine
  • Bromine-Iodine
  • Conductivity in µS/cm and TDS in ppm
  • Total alkalinity
  • Total hardness ( mostly calcium hardness )
  • Temperature in °C
  • Copper
  • Cyanuric acid
  • Iron
  • Nitrate and phosphate
Water analyses pools

Wateranalysis of swimmingpools

Why must we disinfect the water of a swimmingpool or spa?

At places where people come together you can find big amounts of micro-organisms !

Each person carries billions of micro-organisms
Swimmingpools are places of sanitation but also cleanness.
Taking a shower will take away many organisms but not all of them. A complete purification of people whithout damaging their health is not possible.
Spittle contains one billion micro-organisms and excrements contain more then 10 billion micro-organisms .
Without the proper disinfection the water would get a smell and the pleasure of swimming would disappear.
Furthermore we could get infected by pathogenic bacteria by one person to another. The rule becomes then: My bacteria infects you and vice versa.

Each bather releases products in the water as urine, hair, skin particles etc.

These organic compounds are used by bacteria as nutrition and they will multiply extensively.
The infection risk depends on the disinfection doses.
You can find many bacteria on the floors. In a dry environment they only can sustain but in combination with water they can multiply with the known consequences.

The human body is poorly equipt for a long stay in the water!

Because of the lack of a thick layer of fat (unlike the warm-blooded water animals) the human body is not protected against a sudden cooling by water.
A sudden cooling toghether with a weaker skin is the reason why humans loose their natural resistance against bacteria.
These bacteria could come from the swimmingpool water but could also already be on the body of the swimmer.

What’s the effect of a good watertreatment?

50% of the incoming contaminants is eliminated by flocculation, filtration and back-washing.
The other 50% must be eliminated by oxidizing and disinfection (=sanitizing):
Oxidizing is the process of distroying dissolved contaminants (organic debris) like ammonia, ureum, proteins, fats and amino acids which come from urine, skin, shampoos etc..
Disinfection(or sanitizing) is the process of destroying bacteria, fungi and viruses.

How can we measure pH?

  • with pH meter: elektrochemical (most reliable)
    • tester : pHep4 (HI 98127)
    • portable meter : HI 991003
    • attention: respect maintenance & calibration
  • with teststrips
    • attention: humidity and sunlight!
  • With testkits:phenol red reagens with photometer or color discs or color cubes .
    • Photometer: HI 83226-02 or HI96725
    • Attention: liquid reagents, avoid sunlight absolutely!

At what temperature do we measure the pH of a spa?

  • Always measure your pH when the water is at the right temperature!
  • Reason: temperature compensation for pH is not the same as for EC.
  • At different temperatures the pH of the water will change because of difference in carbondioxide concentrations or other chemical reactions.
  • pH influences all other parameters, so it’s very important to have the correct pH value and measuring it correctly before doing anything else!

 

How do we measure free and total chlorine?

water analysis

Multiparameter photometer

HI 83326-02

  • Compact, portable/lab photometer – specially designed for swimmingpool and spa water analysis.
  • For the professional swimmingpool installers and maintenance people.

How does a photometer work?

water analysis

Multiparameter photometer

HI 83326-02

  • Compact, portable/lab photometer – specially designed for swimmingpool and spa water analysis.
  • For the professional swimmingpool installers and maintenance people.

Always make a blank first. This is only the water itself to compensate for color or turbidity of the water itself.

  • Carry out blanc measurement by pushing on the zero button.
  • Add reagent(mostly powderpillows) and mix gently.
  • Respect the reaction times (timer button)
  • Then you will have the result in mg/l or µg/l. (read button)

Highly colored or turbid samples must be deluted or filtered before measurement or the phptometer will go <<blind>>.

Cuvets must be clean.

  • Watch out with interferences (mostly not the case with swimmingpool or spa water).
  • Reagents per 100 pcs! Clean cuvet after use immediately
  • Look at expiring date!
  • Validation(checking) of photometer or reagents only with standard solutions.
  • Photometers are more accurat then testkits and teststrips!

ORP or Redox: an indirect measurement of free chlorine!

Redox or ORP is the oxidation-reduction potential of water expressed in mV.

water analysis

Note : ORP measurements can be slow. Pre-conditioned ORP sensors immersed in free chlorine concentrations of 0.2 and 3.0 ppm were found to require a minimum of 10 to 12 minutes to reach a stable reading.

The response of the electrodes to the REDOX reactions that take place on the surface of an electrode depends on the speed of the many reactions that give the potential and the rate at which molecules diffuse through the water.

So the key to successful ORP measurement is patience!

water analysis

pH & ORP tester – HI 98121

  • IP67
  • ORP: +/-1000 mV
  • pH: 0,00 – 16,00
  • temperature: 0,0 to 60,0°C
  • automatic calibration and recognition of buffers
  • Battery status indication and BEPS (Battery error protection system)
  • auto extinction after 8 minutes

Bromine

-Bromine together with an oxidizer also forms HOBr and OBr depending on the pH of the water but it’s a wider active range then chlorine. (upto pH 8,7 still active for 50%)

-It’s a good disinfection & oxidizing compound.

-With organic impurities it forms Bromamines (combined bromine) which don’t smell and still work as a sanitizer.

It’s mostly used as BCDMH (1-Bromo 3-Chloro-5,5 dimethylhydantoin) in tablet form.

Lodine

Iodine

-Iodine  in the form of KI (Potassium Iodide) is dissolved in water together with an oxidizer  to convert it to HOI (Hypoiodious acid). Iodine doesn’t react with ammonia to form Iodamines.

-it doesn’t bleach hair or swimming suits, and eye irritation is practically nonexistent.

-Other chemicals (usually chlorine) must be used in conjunction with iodine to control algae and oxidize organic matter. The sole effect of iodine is to produce bacterie-free-water.

Conductivity (EC)

  • It’s the ability of a material in the water to conduct an electric current.
  • Expressed in µS/cm(microsiemens/cm) or mS/cm
  • Each dissolved product has own specific conductivity
  • Correlationship between hardness and EC :
  • 20 µS/cm = 1 °f= 10 mg/l CaCO3 (with an error of 2-3°f)
  • The correlationship is not valid for water of softeners
  • Method for measuring: with conductivity meter:
    • HI 98312, HI 98130
  • TDS or Total Dissolved Solids is a measure of the total ions in solution. EC is actually a measure of the ionic activity of a solution in term of its capacity to transmit current.
  • In dilute solution, TDS and EC are reasonably comparable. The TDS of a water sample based on the measured EC value can be calculated using the following equation: EC x 0,5 = TDS (mg/l or ppm).
  • For very high concentraties the conversion factor will be higher.

Why measure conductivity of swimmingpool or spa water?

  • It determines indirectly the amount of salt in the spa or swimmingpool water which is equipt with salt electrolyse systems!
    • In swimmingpool: 3 kg salt / m3 (= 3 g salt / l)  + TDS water: 0.3 g/l

TDS swimmingpool water: 3.3 g/l

OR

  • When do I need to back-wash my spa or swimmingpool?
    • Back-wash if EC > 2100 µS/cm or TDS > 1050 mg/l (ppm)

Total alkalinity

  • Alkalinity: it’s the pH-buffer capacity of the water or the water’s resistance to a change in pH. Primarly due to bicarbonates in the water.
  • Expressed in mg/l CaCO3
  • 10 mg/l CaCO3 = 1° FH = 0,56 °DH
  • Two methods for measuring:
  • Photometric with HI 83326-02 up to 500 mg/l CaCO3
  • Titrimetric with testkit: HI 3811 : 0 – 300 mg/l CaCO3
  • Recommended value: 75 – 120 mg/l!

Total hardness ( primarly calciumhardness )

  • Total hardness: it’s the sum of calcium and magnesium hardness. The major part( +/- 80 % ) is mostly calciumhardness.
  • Expressed in mg/l CaCO3
  • 10 mg/l CaCO3 = 1° FH = 0,56 °DH ( 1 °DH = 1,78 °FH )
  • Two methods for measuring:
  • photometric: HI 83226-02 : calciumhardness :
    0 tot 500 mg/l CaCO3
  • Calciumhardness reagent is now HI93720-01
  • titrimetric with testkit HI 3812 ( 0 – 30°FH )
  • Ideal hardness: 100 – 200 mg/l CaCO3
  • If hardness is too high: water becomes cloudy (will go faster at higher pH >8) or scaling.
  • If hardness is too low: corrosion is possible because of no thin layer of calcium to protect against pitting corrosion of metal parts.

Cyanuric acid, copper, Iron and temperature!

  • Cyanuric acid: < 70 mg/l
  • If more then 70 mg/l of cyanuric acid is present the free chlorine will become too stable and the active part(HOCl) of the free chlorine will decrease Also according to WHO it becomes toxic for humans.
  • The DPD method doesn’t see the difference of free chlorine with cyanuric acid or without!!
  • Photometric with HI 83326-02 or HI96725
  • Cyanuric acid has a pH of 4.0
  • Copper: 0,3 – 0,8 mg/l
  • Photometric with HI 83326-02
  • Iron: < 0,2 mg/l
  • Photometric with HI 83226-02
  • Temperature < 32°C for swimmingpool and <37°C for a spa.

Nitrate and phosphate

  • Nitrate < 50 mg/l NO3
  • Phosphate < 2,5 mg/l PO4
  • These two compounds can cause eutrophication and suddenly green swimmingpool water because of rapid algae growth.

->Will be possible to measure with the new generation of

HI83326-02;

Practical examples of solving problems with swimmingpool or spa water.

  • Problem: too much chlorine in the water?
  • The cause:
  • -overdosing because of decolorazing of DPD reagent .
  • DPD reagent decolorazes starting from 10 mg/l free chlorine and give a 0.0 mg/l reading on the photometer with as a result that customers will add more chlorine sometimes.
  • -Overdosing because of defected automatic dosing system (eg broken redox electrode)
  • Solution: use Sodiumthiosulfate(Na2S2O3) or hydrogen peroxide (H2O2)
    • 1 kg Na2S2O3 breaks down 850 g chlorine
    • Example
    • Volume of swimmingpool is 75 m3
    • Free chlorine in the pool is 3,5 mg/l, wanted level of free chlorine is 1,5 mg/l.
    • Free chlorine to be removed is 2 mg/l or 2 g/m3

    75 m3 x 2 g/m3= 150 g chlorine to be removed

    150/850= 0,176 kg or 176 g Na2S2O3 needs to be dosed

    Side effect: slight decrease of the pH.

How can automate my swimmingpool or spa?

AutomatizationL in private sector everything is alowed but…!

  • We have only many, many years experience with chlorine (more then 100 years)
  • New technologies like UV, copper- silver ionisation, hydrogen peroxide, chlorine dioxide, ozon etc… have also advantages and disavantages and furthermore we have little experience on long term with these technologies.

Other technologies

  • Ozone:
  • advantage: -no odour
  • -strong oxidation and disinfection agent
  • -made out of oxygen in chamber of ozonator
  • disavantage: -very expensive and increases the needed amount of chlorine with factor 4

-may not be present directly in the spa or swimmingpool water because starting from 0,05 mg/l it’s already toxic for humans. It’s difficult to measure in presence of chlorine in the water. (an active carbonfilter is necessary to avoid ozone from getting directly in the water)

-can form the harmful bromate (carcinogetic )

Ultra-Violet(UV):

  • advantage: -no odour

-no chemicals needed

  • disavantage: -very expensive and breaks down chlorine

-not a real alternative because it has no oxidizing effect.

-has no residual effect in the water, works only at the spot where the water passes.

-danger of modification of DNA of organisms at the wrong wavelenght

-Radiation doses depends of the purity of the water (no scaling on the lamps)

Copper and Silver Ionisation

  • Advantage : – no odour

– no chemicals needed

  • disavantage: -is mostly wrongly installed and it’s very expensive

-copper battery before the filter and silverbattery after the filter  according to the

Velasques – Cassanova principle.

-silver is very difficult to measure photometrically and can form black deposits on liners.

Hydrogenperoxide (H2O2):

  • Advantage : – no odour

-no harmful aside reactions

-no pH increase effect

  • Disadvantage: -very expensive (must be stabilized with Silver)

– breaks down chlorine (so cannot be used together)

-high concentrations needed for good effect (40 à 80 mg/l)

-It doesn’t work if catalase active bacteria are present

-in very high concentrations (like 30%= perhydrol) it’s very irritating for skin and our respiration system.

Salt electrolyse with NaCl: it’s the same chemistry as chlorine chemistry. We don’t use liquid chlorine but we make out of (Kitchen) salt = NaCl directly or indirectly chlorine in the pool. A correction of the pH is thus still slightly necessary!

Chlorine gas is formed at the anode (+) and NaOH at the cathode (-). The chlorine gas reacts with the water to form HOCl. pH will decrease but the forming of NaOH will level the pH mostly. Also hydrogen gas will be formed.

Chlorinedioxide (ClO2):

  • A yellowgreen gas with a chlorine and irritating smell in its pure form. It dissolves very easy in water and faster then chlorine.
  • Chlorinedioxide is unstable and must be kept cool and produced locally. It’s to dangerous to transport as a gas (>10% in air is explosive)
  • Produced mostly like: 2NaClO2 + 2Na2S2O8—>2ClO2 + 2Na2SO4
  • Advantage : – no odour in diluted form in water

-no harmful aside reactions

-no pH increase effect

-it’s active between pH 5 and 10 at concentrations between 0,5 and 2,0 mg/L

-it can easily penetrate biofilms.

  • Disadvantage: -forms chlorite(ClO2-)and chlorate (ClO3-) and finally NaCl

– less effective againt Rota virus and E. Coli

-more expensive then chlorine.

The new poolcontroller BL121-02 & BL122-02

BL121-122

->BL121-02 is basic version without flowcell

->BL122-02 is with a flowcell on a panel

Both versions are delivered completely with combo electrode, aspiration & injection tubings,

Aspirationfilters (2), injectors (2), buffers pH 7,01 & 4,01 sachets, HI7022M, saddles and manual.

The new poolcontroller BL121-02 & BL122-02

->Unique sales arguments:

  • -master-slave: pH has always priority above chlorine. It makes no sence to inject chlorine if pH value is too high
  • -time out alarm to prevent overdosing (programmable according to the size of the pool) if electrode is malfunctioning
  • -delay time for pH and ORP.. Redox electrodes have by definition a slow response time
  • -Display shows simultaneously pH, ORP and temperature.with backliight
  • -the unique digital combo electrode HI1036-1802: combo pH, ORP, temperature electrode with matching pin. Faster installation time and no competition (no BNC connector).
  • Silent peristaltic pumps with programmable flowrate (0,5 to 4,5 l/h) for spa’s, small pools and very big pools.

Degassing is not necessary when barrels of acid or chlorine are empty.

  • – digital combo electrode so cable length is not an issue (law of Pouillet).
  • -matching pin technology: no interferences from current loops.

Electrodes with BNC have no mathing pin possebilities.

  • -do not use our combo electrode in salt water!

for salt water you need golden ORP sensor.

Controller has:  GLP functions and data memory (export through USB)

boot loader: updating software is possible

low and high alarms are programmable

proportional dosing

analog output

competition: many brands

  • .Seko, Prominent, Hayward, iAqualink (Zodiac-Jandy), Intellipool (Pentair), Siemens, Aqualink (UK), Watersense (Czech) , Etratron (It), Dinotec etc;;;
  • Most of our competitors use BNC connectors for pH and ORP electrodes:
  • HI1286A
  • HI3214P
  • Or without cable and PG13,5:
  • HI1210T
  • HI3210T
  • Amplified :
  • HI6291005
  • HI6293005

The Water Balance and Langelier Index

Pool water characteristics need to be maintained in a balanced state to avoid numerous issues. Measuring certain variables is extremely important to predict if the water is corrosive or will cause scaling.

A saturation index developed by Dr. Wilfred Langelier is widely used to predict the balance of swimming pool waters. It represents the estimation of a solutions ability to dissolve or precipitate calcium carbonate deposits. A certain level of this precipitation (filming) is desired to insulate pipes and boilers from contact with water. When no protective filming is formed, water is considered to be corrosive. On the other hand, too much filming can develop into scaling and incrustation of the pipes.

In the treatment and monitoring of pool water, the pool manager must ensure that related parameters such as alkalinity, hardness and pH are carefully monitored in addition to sanitizing chemicals.

Langelier Index

The Langelier Index is a powerful tool to calculate the water balance, and to predict corrosion or scaling problems. Theoretically, a LI of zero indicates perfect water condition for swimming pools. If LI>0, scaling and staining of the water is present, and if LI<0 the water is corrosive and highly irritating. A tolerance of ±0.4 is normally acceptable.

The Langelier formula is expressed as: LI = pH + TF + HF + AF – 12.5
Where:
LI = Langelier Index (also called Saturation Index)
pH = pH of the water
TF = temperature factor
HF = hardness factor, log (Ca hardness, ppm as CaCO3)
AF = alkalinity factor, log (alkalinity, ppm as CaCO3)
To calculate the exact Langelier Index of your water please use the
WATER INDEX reference tables.
For most pools, water is balanced if:
• The pH value is maintained within the recommended ranges of pH
7.2 – 7.6
• Ideally, the Alkalinity should be maintained within a range of
80 – 125 ppm
• The Calcium Hardness should be maintained within a range of 200 – 400 ppm.

Ozone

Ozone is a very strong oxidizing agent that destroys organic compounds that are especially difficult to oxidize. It allows the pool manager to very efficiently remove combined chlorine without frequently refreshing large amounts of pool water. By the time the water passes through the filter units, ozone has already completed sanitizing, and it is not effected by the pH level.

Mainly because of its strong oxidizing power, the return water may contain trace concentrations of ozone. It imperative to know that ozone is very unstable, so to ensure thorough sanitization of the water, low-level chlorination remains necessary.

Calcium

The presence of calcium in the system is desired to ensure filming on those places where the temperature is relatively high, like in boilers and pipes transporting warm water. Scaling must be avoided because it reduces heat transfer and pump capacity, and causes cloudiness in the water.

It is recommended to maintain the calcium hardness value within the range from 200 to 400 ppm as calcium carbonate (CaCO₃).

Alkalinity

Alkalinity is the measure of the total concentration of alkaline substances, mostly bicarbonates, dissolved in the water. The higher the alkalinity, the more resistant the water is to pH change. At the same time, high alkaline water is a major contributor to scaling problems like incrustation in filtration equipment, pumps, and piping.

It is recommended to maintain the alkalinity value within the range from 80 to 125 ppm as calcium carbonate (CaCO₃).

pH

The pH of the water is an important factor since at lower pH levels the corrosion rate increases. If the alkalinity values are sufficiently high, it will not be difficult to control the pH. Most pool managers prefer to keep the pH between 7.2 and 7.4 to best maintain low corrosion rates and a sufficient activity of chlorine.