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Pool and Spa Maintenance: Balancing the Water

Problems in pool and spa water.

Problems in pool and spa water.

Why Pool and Spa Water Must be Balanced

Serious, sometimes life-threatening, illnesses can be spread by water that is not properly maintained. Your expensive pool or spa and all of its equipment is under threat from unbalanced water.

Also, the water can become plain yukky if it is neglected! By that highly technical word, I mean, algae, slime and unpleasant smells become unwelcome companions very rapidly.

On this Page

  • Sanitizers - Chlorine, Bromine, Biguanides (eg Baquacil, Soft Swim)
  • Chlorine and non-chlorine 'shocks' to clear out organic contaminants
  • Non-Chemical Sanitizers- ozone and ionizers
  • Acids and Alkalis
  • Total Dissolved Solids
  • Total Alkalinity
  • Water Hardness

Things to Monitor Regularly

Keeping water in a swimming pool or spa healthy and balanced is a question of understanding what is in the water, how the various chemicals can be measured and what needs to be added to get things to the right level.

There are five important properties of pool spa and hot tub water that need to be routinely monitored: the sanitizer, total alkalinity, pH level, hardness, and total dissolved solids. With the right chemical kit or test strips these can be measured quickly and easily.

The difficult part comes when you adjust one of the components and find that it has affected other components in a way that you don't want. This is why people talk about 'balancing the chemicals' in a spa or hot tub. Get the proportion of chemicals right and the water is balanced, healthy, safe and fresh. This needs a little practice but is pretty simple once you grasp the essential facts.

First off, it's worth looking at the kind of chemicals used in pool spas and hot tubs and what their job is.



Sanitisers do what they say they do. They kill bacteria and anything else in your pool or spa that might threaten your health. They also help to stop algae growth.

Chlorine Sanitizer

The commonest and cheapest sanitizer is chlorine. For spas and home pools, chlorine comes in a liquid or solid form. Larger pools may use chlorine gas.

Liquid Chlorine

Liquid chlorine is sodium hypochlorite dissolved in water and has the advantage of being cheap and very easy to use. The typical spa product has about 12% of available chlorine. The rest is water and sodium chloride (common salt). Sodium hypochlorite is also the main ingredient in normal household bleaches but don't use household bleach as a sanitizer unless you are sure it contains nothing but sodium hypochlorite. Many brands of household bleach contain detergents or phosphates which will promote algae growth.

When the chlorine comes into contact with any organic material like bacteria or dead skin flakes the chlorine attacks the organic material and breaks it down (technically, the organic material is oxidized). Common salt (NaCl) remains behind in the water.

In storage, it needs to be kept cool and away from sunlight. Liquid chlorine should be used within a few weeks of purchase.

Calcium Hypochlorite

This is available in granular or tablet form. Like liquid chlorine, it deteriorates in sunlight or hot conditions. It is relatively slow dissolving and can leave unsightly mineral residues in the water-often it is sold in a fabric bag to prevent this from happening. It is 65% chlorine and will make water more alkaline.

Dichlor (Sodium Dichloro-s-Triazinetrione)

This is a solid product with about 60 per cent available chlorine. It is weakly acidic. This is a popular choice for home use, as it is stable, doesn't affect water pH too much and is safer than the Trichlor described below.

Trichlor (Trichloro-Triazinetrione)

This product usually comes as tablets or sometimes as granules. It is slow dissolving which can be an advantage if you want to keep water fresh while you are away. It is often used in automatic sanitizer delivery systems.

It has 90 per cent available chlorine and is the most expensive of the chlorine sanitising products. It is also the most highly acidic and pH will need to be adjusted whenever it is used.

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For professional spa and pool technicians, this is the chemical of choice for tackling serious algal problems. It also has the advantage of being very stable so it can be kept for long periods without deteriorating.

Safety Issues with Chlorine Sanitizers

All strong chlorine solutions will attack skin and natural clothing (eg cotton or wool) and should be treated with respect. Gloves and eye protection are recommended for handling very strong chlorine solutions. Trichlor is a lung irritant.

Cyanuric Acid Stabilizer

Cyanuric acid stabilizer (sometimes called 'conditioner') helps maintain levels of free chlorine in the pool or spa water. Without CYA, up to 90% of free chlorine can be destroyed by sunlight in as little as three hours.

CYA Levels should be between 30 and 80 ppm. Too much will stop the chlorine working at all and too little won't offer enough protection.

Chlorine sanitizers compared.

Chlorine sanitizers compared.

Chloramines, Free Chlorine and Total Chlorine Load

Chloramines are formed when chlorine reacts with ammonia from sweat or urine in the water.These are the chemicals that give the strong smell and stinging eyes associated with chlorine use. If water is well maintained, chlorine sanitizer will cause little irritation.

Chloramines don't kill bacteria so ammonia is said to 'tie up' chlorine. Only the free chlorine is able to act as a sanitizer.

To manage a hot tub or spa successfully it is important to know both the free chlorine levels and total chlorine levels. High total chlorine indicates the need for a chlorine 'shock' (see below).Test strips from your local or online supplier allow you to measure free and total chlorine quickly and easily.

Different Folks, Different Names

One area of confusion in spa and hot tub maintenance is that people use a lot of different names when talking about the same thing. When it comes to chlorine sanitizer, this is especially so.

Free Chlorine=Available Chlorine=Residual Chlorine

Total Chlorine=Chlorine Load= Combined Chlorine.

There are only ever two chlorine measurements to worry about in pool or spa water. Just pick a name for each and stick to it!

Chlorine Shock (or Super Chlorination)

Spas and hot hubs need a regular 'shock' treatment to clear out organic material. Chlorine shock is OK to use where either chlorine or bromine is the sanitizer. With biguanide sanitizer always use hydrogen peroxide as a shock (see below).

A chlorine shock needs to be applied at anything from weekly to monthly intervals depending mostly on bather load. Check packaging of your chlorine product for doses. 10 ppm of free chlorine is usually strong enough as chlorine shock. Non-chemical sanitizer systems like ozone generators and ionizers reduce the need for shocking.

Essentially, a shock is needed whenever there are any obvious problems with water quality such as cloudiness, smell or algae and is a good idea after any heavy use of the pool, spa or hot tub.

After a chlorine shock, keep people out of the water for at least 24 hours and test the water to make sure it has returned to less than 5 ppm of chlorine before giving the all clear to users

Chlorine chemistry

Chlorine chemistry

Non-Chlorine Sanitizers


This is used as an alternative to chlorine when people don't like the odors produced by chlorine. It is also more stable than chlorine at the high temperatures found in hot spas. It can be applied in granular or stick form. A small amount of chlorine is often used as a catalyst (ie to activate the bromine) but non-chlorine catalysts are also available.

One advantage of bromine sanitizer is that when the bromine is 'tied up' by organic contaminants or ammonia from sweat, it can be easily revived. Shocking once a week or so (depending on the number of bathers) with chlorine or non-chlorine shock will bring free bromine levels up, without necessarily having to add more bromine.

The ideal range for bromine is 2.0 to 4.0 ppm.

If you overdose with bromine, the levels will fall fairly slowly. Supply shops sell chlorine and bromine neutralizers if you need a quick reduction.

Biguanide eg. Baquacil, Soft Swim

To use this sanitizer effectively read all the instructions that come with the product. The normal regime is a monthly shock with hydrogen peroxide and weekly doses of Biguanide to maintain a level between 30 and 50 parts per million (ppm). Dissolved metals need to be removed from the spa or hot tub (with something like 'metal out') and great care used with cleaning agents.

Introducing any product containing chlorine into the water can result in brown, discoloured water and deposits on the sides of the spa. It is not compatible with ozone generators.

Advantages and Disadvantages of Biguanide

Biguanides are not usually recommended for spas or aerated pools.

Fans of biguanide sanitizer say it is less irritating to skin, eyes and nose. They also point out that it is more stable so that water needs less maintenance. Detractors claim that biguanides are not as effective at killing bacteria and it is difficult to be sure that the correct levels are present in the water. Filters choke up more quickly and need cleaning more often.There is an interesting discussion between pool users here:

Non-Chemical Sanitizers


Copper ions are effective in killing algae. Silver ions are effective in killing bacteria. Ions are simply electrically charged particles that are generated by placing electrodes in the pipework connected to a low voltage dc supply. They can cause staining on pool and spa surfaces if not properly managed.


Introducing ozone into the water will kill bacteria and reduces the amount of water sanitizer required.It improves the smell, feel and clarity of the water and helps clear scum and oils.

Ozone is generated by either passing air over a powerful ultraviolet light or by passing it through a corona discharge (a sort of lightening storm in a box). The high energies convert ordinary oxygen into ozone, a very reactive molecule that attacks organic material.The need for sanitizer is reduced not eliminated.

Problems with Algae

Other Important Water Properties

Acids and Alkalis

pH is the scale used to measure how acid or alkaline water is. 7 is neutral. Anything less than 7 is acidic, anything above 7 is alkaline. Spas and swimming pools need to kept between 7.2 and 7.8.

If spa or pool water becomes too acidic, the water will attack and corrode metal fittings, sometimes leading to water discolouration. If water become too alkaline it encourages scale to form on the pool or spa sides and equipment. Heater failure is a common result.

pH also has health implications because it has an impact on how well sanitizers work.

Acid- either in liquid or granular form-is used to adjust pH. Test kits for pH are available from spa and pool supplies stores. Adding too much acid means you will need to correct with alkaline products like 'alkahli up'.

pH anchors can be used to lock in pH levels but these affect your ability to adjust water hardness.

If the pool or spa has plastered or tiled walls, alkaline lime in the plaster or grout is constantly dissolving so more monitoring of pH may be needed.

Total Alkalinity

This is a measure of all the chemicals in the water that have a potential to be alkaline. This needs to be measured and the alkaline materials (like dissolved lime) need to be neutralized before pH is adjusted. This will save a lot of sanitiser and acid use in the long run. Alkali neutralizers can be bought from any good spa or pool supplier. Excess alkalinity will contribute to lime scale deposition which in the worst cases blocks jets and pipes. Total alkalinity outside of the normal range can make pH fluctuate wildy.

Total Dissolved Solids (TDS)

TDS is a measure of all the chemicals in a spa and is easily monitored with test strips. It increases with time as more and more chemicals are added and also as a result of evaporation. Once TDS exceeds 2000 ppm, balancing a pool is difficult and requires excessive chemical use. The pool needs to be drained partially and refilled with fresh water.

Never drain a pool with a vinyl liner by more than a third. The liner will shrink and, instead of stretching when the water is replaced, it will tear.

Water Hardness

Tap water containing a lot of dissolved calcium salts is usually called 'hard' because it is difficult to produce a lather with soap.

Water hardness can affect pools in two ways. If the water is too soft it can gradually dissolve metal fittings and cause water discolouration. If it is too hard it can result in scale deposits on pool or spa surfaces.

Water hardness can be measured with test strips and adjusted with products like Water Hardness Increase or Scale and Stain Control (decreases water hardness). If you use a pH anchor to maintain a constant pH do not use these products. Reduce water harness by draining the pool and refilling.

Water Hardness

Water is said to be hard when it contains a lot of calcium or magnesium salts. The most obvious sign is that it is difficult to get a lather when washing with soap.

Water that is very soft can slowly dissolve metal components in pipework and pumps. In plaster-walled or tiled pools and spas it will dissolve cement and grout. Water that is very hard will deposit lime scale, clogging pipes, jets and filters. If left unchecked lime scale can cause failure of pumps and water heaters.

Water softening agents are available but often the only way to reduce water harness is to drain or partially drain the water and refill with fresh. Calcium chloride can be added to increase water hardness.

If you use a pH anchor, avoid using water hardness adjusting chemicals.


Will Apse (author) on January 21, 2012:

Some water, especially well water contains a lot of dissolved metals like iron (a prime suspect if you are getting reddish stains). Copper can be leeched from copper fittings and pipe work.

Mild acids like citric acid (lemon juice, for instance) or acetic acid (vinegar) are often enough to clean the stains off.

Also, some chemicals can be used to take the metals out of solution. The metals bind to chelating agents and fall to the bottom of tub or just get filtered out. BioGuard Pool Magnet is one product- how well it works and how safe these kinds of chemical are, I wouldn't like to say.

The tried and tested way to get rid of iron manganese and also sulfur is a greensand filter.

This page has some good info on these kinds of filter:

hot tub on January 21, 2012:

why is my hot tub generating a rust colored particle sticking to sides of hot tub?

dankoz51 from Chicago on January 20, 2012:

Roxy, yes you can get sick. Dirty hot tub and/or poolwater can be very dangerous. Though its not normally the case its the whole reason to use chemicals.

Roxy on September 20, 2011:

Can u become sick from hot tub usage if not enough clorine is in it?! I went in without knowing and water smelled old n smelly. That night I got stomach cramps and nausesnous. It's weird and three days later it's only gotten worse.

Will Apse (author) on September 10, 2011:

You are right, SAL. They don't mix at all. You could easily find you have a pool of brown slime!

SAL on September 10, 2011:

What would happen if chlorine granules were added to a pool using the Baquacil system? I'm trying to explain to my spouse that the two chemicals are not compatible, but he keeps wanting to add chlorine to the pool because that is what he is used to using.

Will Apse (author) on January 01, 2011:

The better your ionizer and the better your ozone generator, the fewer the chemicals of any kind you need, Pamela. Some Australian pool and spa experts reckon a combination of these two devices is all you need but I would be a little wary of that assertion.

This page makes a good case for their use for anyone interested:

Biguanides are the main alternative to chlorine and bromine as I said above but they are more expensive!

Pamela on January 01, 2011:

For those with low thyroid function (hypothyroidism) and anybody concerned about maintaining thyroid function (you'd be surprised at how important this little gland is!), neither chlorine nor bromine are acceptable as each reduces thyroid function. What alternatives are then available that don't cost an arm and a leg for spa maintenance?

Will Apse (author) on November 13, 2010:

Chlorine is a powerful chemical, Heidi. I once used some undiluted bleach to clean some stains on a cotton shirt. Of course, the chlorine in the bleach burnt straight through the cotton.

We all live and learn.

Heidi on November 12, 2010:

I wish I would of read this sooner. We went in just a few hours after a chlorine shock was done. All six of us had red spots on our skin the next day. Unfortantely my friend and her two children went to a Medi clinic and were wrongly diagnosed with chicken pox. They all wre prescribed anti-viral drugs. I found this out a week later. Very informative article.

Will Apse (author) on November 10, 2010:

I would recommend a good ionizer and an ozone generator, Kalamazoo. You will only need a tiny fraction of the chemicals that you need without them. They will pay in the longer term and the water will feel way better.

After that the chlorine route is inexpensive and once you get used to balancing the water it won't smell bad.

B.Kalamazoo on November 09, 2010:

Sorry, forgot to say I have a 500 gal hot tub, never seem to get the water to not have a stong chemical smell. Its good for about the first week after I fill.

B.Kalamazoo on November 09, 2010:

Could you list the start up program and list of chemicals to use on a weekly basis. So many article you could spend a fortune for all the chemicals stores recommend. What brand is recommended?

Robert James on November 04, 2010:

Nice job explaining all about the chemicals. Bromine lasts longer than chlorine so is the better choice for hot tubs. We don't sell spa chemicals, but get questions all the time. Thanks for your clear explanation and research!

kubth from UK on September 24, 2010:

Great info about the pros and cons of various Hot Tub chemicals.

tom.staton from Oxford on September 23, 2010:

i thought bromine and chlorine are as good as each other, its just bromine resists more heat that's why it is used in hot tubs more.

Will Apse (author) on September 06, 2010:

Folliculitis is an infection of the hair follicles. I hope your hot hub doesn't have hair Jaco.

Jaco Henn on September 05, 2010:

I need some help please, my hot tub has a bacterial infection called folliculitis, how do I get rid of it?

jon talon on August 31, 2010:

Tired of being ripped off for spa chemicals that are the same as pool chemicals; just adjust your dosing. Pool mps non-chlorine shock 3-6 dollars per pound, Spa mps non-chlorine shock..15-17 dollars for TWO POUNDS!

Will Apse (author) on August 10, 2010:

I'm glad you said that Richard. It is quite a big slab of information and it was hard work trying to make it understandable!

Richard Stephen on August 10, 2010:

Thanks so much for this hub. I've had some trouble getting a grip on my pool chemistry and you did a great job explaining things in a way I could understand. Keep up the good work!

Paul on July 08, 2010:

We have got a new(ish) Spa and cannot 'take' chemicals - without coming out in blotches anyway - thee non-chemical pack we have purchased has NOT solved the problem; grit, some smell. Does anyone have a solution?

Casey Ollson on June 03, 2010:

Actually, bromine is better for hot tubs and chlorine is better for pools!

coolSam on April 15, 2010:

hey, your post is interesting, do you think there are any substitute for chlorine or bromine for the pool?

thanks anyway!! :D

Karen Reader on April 02, 2010:

You are right about keeping your pool water balanced. It just doesn't need chlorine like some folks think!

splashpads from USA on March 28, 2010:

Dang this is a ton of good info thanks

Inflatable Hot Tub on February 08, 2010:

Great information, I think some people forget how important hot tub chemicals are.

Will Apse (author) on January 16, 2010:

I would keep flushing and also check and back wash the filter. If the filter is looking grey you might need a new one. If you have a sand filter the sand might need changing (sand can lose its edge).

One of the best things to do if you are looking after a pool is get a relationship with a local pool store. Usually someone in the store understands pools and can offer good advise.

Local help is valuable because they know what the local water is like. Maybe that 'grit' is a precipitate of calcium salts from hard water. If it is, a pool store can suggest remedies.

Nat on January 16, 2010:

Hi ive just moved into a rental with a home spa, and have never had one before.a lot of gritty stuff has been coming out of the pipes when i flush it out with the spa cleaner i brought.It just doesn't seem to be getting cleaner..what do i do?

Kenny on December 17, 2009:

Not many people know the importance of proper maintenance for their pools, spas, etc. Thanks for sharing such comprehensive information about the contaminants in the water.

Amy Appleton on November 09, 2009:

Is salt better than bromine?

Will Apse (author) on November 03, 2009:

Some manufacturers claim that their biguanides are OK with ozone generators. The problem is the chemical is organic and easily oxidized- this is why chlorine and biguanides don't mix.

Ozone is one of the most potent oxidising agents around. It will break down biguanides and result in a slow gumming up of pipes and pumps.

Tom on November 03, 2009:

Why are biguanides not compatible with ozone generators?

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