Sanitizing Chemicals | Pool Chemicals | Table

Superchlorination or Shocking

- AKA ‘Shock dosing’

Warm water presents ideal conditions for algae to establish themselves in your pool and the slightest inattention on your part can result in a nasty, unhealthy green mess that can take the untutored days or even weeks of hot, sweaty labour to clean up

An algae bloom, especially if it is left untreated for a few days, is very bad news indeed

As algae proliferates it strips carbon dioxide from the water

The pH of the water then rises and the Sanitizing Chemicals become less effective – allowing the algae to flourish – which raise the pH – which makes the chemicals even less effective - which allows the algae to grow even faster. . . you can probably guess how this might continue . . .?

When pH reaches 8.6 the minerals dissolved in the water precipitate out (the water turns milky) - coating the tiles, the plumbing and the filter media with lime-scale

The extra minerals now available in the water provide building materials for more and more algae and the process accelerates

The best defence against algae bloom is routine, systematic Superchlorination - the secret ‘right-hook’ of the Pool Professional

Superchlorination or ‘shock dosing’ refers to the addition to the water of anything that will remove or destroy ammonia and nitrogen compounds by oxidation - traditionally this has been a Chlorine compound

There are now several Non-chlorine Shock products available

Organic matter and ammonia compounds can get into a pool from many sources

Swimmers and bathers are major contributors with their bodies giving off skin flakes, mucus, saliva, sweat, urine and faecal matter

Dust, fertilisers, algae, leaves, twigs, certain water-treatment chemicals and rain also introduce contaminants into the water

(Here’s one unusual way that a pool can become contaminated)

Instructions for Superchlorination

Every 2 weeks, as a matter of routine, add liquid chlorine (Sodium Hypochlorite) or Calcium Hypochlorite (pre-dissolve Calcium Hypochlorite in pool-water before application) at dusk with the Rotary Valve set to ‘Filtration’ and with the pump on and the pool-cover OFF

High Chlorine levels can weaken and destroy a pool-cover very quickly, therefore keep the cover off until Chlorine has returned to normal levels of 1-3ppm

Add the chemical to the water at the jets to promote rapid mixing

Run the pump for 4 hours to circulate the superchlorination chemicals

The pool is out of action for twelve hours after superchlorination; therefore you apply it when you have finished using the pool for the day, secure in the knowledge that the water will be sanitized and safe the next day
If you want to use the pool sooner than after 12 hours, you can add Sodium Thiosulphate to reduce high levels of Chlorine

Dosage rate for Superchlorination is 2 litres of Sodium Hypochlorite or 1 Kg of Calcium Hypochlorite per 50m³ of pool-water

Dosage rate for Superchlorination is ½ US Gallon of Sodium Hypochlorite or 2 lb of Calcium Hypochlorite per 10,000 US Gallons of pool-water

Liquid chlorine has a pH of around 11.6, so this amount of Chlorine will alter the water balance and the pH will rise

To counteract this rise add 1 litre of liquid acid at the same time

Add the acid at the Jets with the pump running but wait a few minutes after adding the Sodium Hypochlorite to allow it to disperse first

In addition to regular fortnightly treatments, carry out superchlorination after a thunderstorm or if the pool is subjected to unusually heavy pollution e.g. a child having an ‘accident’ in the water

Check the water chemistry, and add chemicals, little and often for best results

Always wash your hands immediately after handling pool chemicals

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Chloramines

- what's that awful smell?

Chlorine and Bromine combine with ammonia and Nitrogen compounds to form ‘-amines’.

Chloramines smell bad, they are eye and body irritants and they are also poor disinfectants

Organic wastes build up and become sources of irritation

Bromamines do not have an odour problem and are as effective as free bromine for disinfection

Dealing with the problem of combined Chlorine requires testing the water to see how much of the Chlorine in the water is 'free' and how much is 'combined'

The commonly used Reagent test-kit will not perform this task. It can only tell you the total Chlorine level and can't differentiate between free and combined Chlorine

However, a DPD test kit or a syringaldazine test strip will do the job

Chlorine reacts with Ammonia and destroys it. When Chlorine is introduced into swimming pool water it instantly forms Hypochlorous Acid (HOCl or free Chlorine) which dissociates (splits up) into H+ and OCl-, the ratio of dissociation depends upon the pH of the water

The OCl- is a strong oxidizer and will oxidize the ammonia to form a combined Chlorine compound known as monochloramine (NH2Cl) and OH-

More Chlorine (as OCl-) is required to continue the oxidation of the Nitrogen or ammonia

If no more Chlorine was in the pool or added to it, the pool water would have a large amount of combined Chlorine as monochloramine rather than the desired free Chlorine

As more Chlorine is added, the monochloramine is now oxidized by the additional Chlorine as OCl- to form dichloramine (NHCl2 + another OH-)

The dichloramine is again oxidized by OCl- to form trichloramine (NCl3 + another OH-)

The trichloramine is unstable and breaks down to simple nitrogen and chlorine, thus completing breakpoint chlorination

Superchlorination to truly achieve the destruction of all organic waste can be very tricky

If insufficient Chlorine is added the combined Chlorine problem is only made worse. When this happens, eye burn and skin irritation are raised to very high and uncomfortable levels

If too much Chlorine is added, it may take days to drop to safe levels (less than 4 ppm) before bathing can be resumed

It takes 7.6 parts by weight of Chlorine to oxidize 1 part of ammonia. Other organics or products in the water will also consume some of the added chlorine so that 7.6 parts is not enough

10 parts of Chlorine for each part of ammonia is generally accepted as being the required amount

Dirty and contaminated pools could take up to 25 parts or more of Chlorine

As a general rule of thumb, the addition of 10 times the combined Chlorine level will achieve breakpoint

So, if the water has 0.5ppm of combined Chlorine by test, you will need to add 5 ppm or more of Chlorine to destroy the combined Chlorine

Each commercial Chlorine product provides a different amount of available Chlorine when added to water, so read the instructions first

In a typical 50,000 litre (13,000 US Gal) pool it will take about 0.5 Kg or 1 pound of available Chlorine to achieve 10 parts per million

Superchlorination raises the level of free Chlorine to between 6 and 10 ppm. Use a non-stabilised form of Chlorine (Sodium Hypochlorite or Calcium Hypochlorite) or Non-chlorine Shock

We supply all plant and equipment featured on this website. All our work is Guaranteed; Parts and Labour

Note: - Please contact our recommended pool professionals for supply and installation of all pool-related services: -

Andalusia and the Costa del Sol - Pool Safety Spain

Nerja area - This email address is being protected from spambots. You need JavaScript enabled to view it.

*We only offer Quotations: - a fixed, agreed price that cannot, and will not, be increased. We do not give 'estimates', as an estimate offers the client no guarantee of final price

Ken Walker - MyPoolGuru©

Cyanuric Acid

- Chlorine Stabilizer

Cyanuric Acid (CYA) is not a sanitizer as such; it is a chemical that protects Chlorine from the destructive effects of the UV rays of sunlight

Ultra-Violet (UV) light degrades Chlorine by a chemical reaction in which Chlorine molecules are destroyed. On a bright sunny day 90% of the active Chlorine can be destroyed by UV in just a couple hours unless CYA (stabilizer) is also present to protect it

Hypochlorous acid (HOCl) and hypochlorite ions (OCl-) closely attach to the free bonding sides of the CYA molecule and, whilst attached, are not degraded by sunlight

CYA acts like a "buffer" - it stores Chlorine and releases it to kill bacteria and algae

However, an excess of CYA in the water (over 100 ppm) stores up the Chlorine which is then not available to sanitize. Keep levels of Cyanuric acid below 80 ppm by periodic replacement of part of the water

A level of CYA of 30-50 ppm is recommended and this level will extend the life of your Chlorine, making it last 3-5 times longer

If your regular Sanitizer is Calcium Hypochlorite or Sodium Hypochlorite, you'll need to add CYA to protect it

To achieve 40 ppm add 2 Kg (4 pounds) of CYA for each 50m³ (13,000 US Gal) of pool water

‘Stabilized’ Chlorine products (Dichlor or Trichlor) do not require the addition of CYA as they produce it when dissolved in water

PS - Cyanuric Acid contains neither Cyanide nor Urine, despite what you might have been told by a well-meaning neighbour

We supply all plant and equipment featured on this website. All our work is Guaranteed; Parts and Labour

Note: - Please contact our recommended pool professionals for supply and installation of all pool-related services: -

Andalusia and the Costa del Sol - Pool Safety Spain

Nerja area - This email address is being protected from spambots. You need JavaScript enabled to view it.

*We only offer Quotations: - a fixed, agreed price that cannot, and will not, be increased. We do not give 'estimates', as an estimate offers the client no guarantee of final price

Chlorine Gas

Chlorine gas is a very potent sanitizer and is the sanitizer of choice in most large public pools due to its extreme effectiveness and economy

The use of Chlorine gas can present problems as it is a toxic substance that is heavier than air and can therefore accumulate in poorly-ventilated pump-rooms

Chlorine gas is a pulmonary irritant with intermediate water solubility that causes acute damage to upper and lower respiratory tract

Concentrations of 2000 ppm causes immediate respiratory arrest and just 150 ppm for one hour is lethal for babies and infants

Chlorine gas supports combustion in the same way that oxygen does Chlorine Gas warning label

Pool Companies that supply or maintain Gas Chlorination equipment (or the gas itself) must be issued with a license by the relevant Health and Safety authorities

For these reasons it is probably best to leave this one to the pros!

We supply all plant and equipment featured on this website. All our work is Guaranteed; Parts and Labour

Note: - Please contact our recommended pool professionals for supply and installation of all pool-related services: -

Andalusia and the Costa del Sol - Pool Safety Spain

Nerja area - This email address is being protected from spambots. You need JavaScript enabled to view it.

*We only offer Quotations: - a fixed, agreed price that cannot, and will not, be increased. We do not give 'estimates', as an estimate offers the client no guarantee of final price