'Official' Pool Chemistry

Disinfection Oxidation
Algaecides pH
Alkalinity Calcium
Stabilizer Metals
TDS Temperature


Disinfection and sanitation

Maintain an adequate sanitizing residual of a primary sanitizer:

Sanitizer minimum maximum test
Chlorine 1.0 ppm1 3.0 ppm 3x week
Bromine 2.0 ppm1 7.0 ppm2 3x week
PHMB* 30 ppm 50 ppm 1x week
Sildate** ? ppm ? ppm ?

All chlorine compounds increase chlorine; all bromine compounds increase bromine. But they vary in what else they add to the pool water. For example, 'dichlor' (sodium dichoroisocyanurate) adds stabilizer and not much else but HTH (tm) (calcium hypochlorite) adds alkalinity, calcium AND raises the pH somewhat.

One more thing. The NSPI does not say much about it, but the NSPI, the EPA, the FTC, and others agree on one thing: there are two, and ONLY two primary pool disinfectants -- chlorine and bromine -- with one exception listed below. And they do NOT include copper or silver ionizers, in any form. There is only ONE pool sanitizer -- PHMB -- a lower classification, which still indicates significant performance in maintaining pool sanitation.  Virtually all of the so-called chlorine free products , if you read the fine print, aren't They still require chlorine or bromine. (PHMB only works with itself).


*PHMB is the ingredient in Baquacil (tm) and Softswim (tm)

** Sildate is a trademark of N. Jonas Co. and is a silver based product which has recently gained EPA approval as a pool disinfectant. At present, I know very little about the product, other than having some reports of staining. However, this registration does NOT change the status of ionizers which contain silver: they are NOT EPA registered as either disinfectants or sanitizers.


Maintain an adequate sanitizing residual of a primary oxidizer:

Oxidizer minimum maximum test
Chlorine 1.0 ppm 3.0 ppm 3x week
Bromine 2.0 ppm 7.0 ppm 3x week
peroxide 25 ppm 50 ppm 1x month
?* ? ? ?

Obviously, if you are using bromine or chlorine, you don't have to add it again. But PHMB is NOT an oxidizer, so you must use peroxide. Copper systems -- whether ionizers, skimmer pills, or liquids -- are NOT oxidizers, so you must use chlorine or bromine. The so-called oxy-shocks (persulfates and perborates) can be used, but they are at least 5x as expensive as chlorine per unit oxidation, AND they oxidize ammonia compounds to nitrates (algae fertilizer)!

However, periodic 'shocking' with chlorine or bromine is often recommended for a variety of reasons, with single doses range from 3 to 10 ppm.


* The Sildate product, mentioned above, is not an oxidizer. I do not know what oxidizers are required or are compatible with it.


Maintain an adequate sanitizing residual of a primary oxidizer:

Algaecide minimum maximum test
Chlorine 1.0 ppm 3.0 ppm 3x week
Bromine 2.0 ppm 7.0 ppm 3x week
L quat* - ~ 30 ppm 1x week
copper 0.2 ppm 0.4 ppm 1x week

*Branded linear quat mixture required with PHMB systems

Obviously, if you are using bromine or chlorine, you don't have to add it again. Chlorine is the most effective all purpose algaecide. But PHMB is NOT an algaecide, so you must use peroxide.

The algae in your pool is partially resistant to whatever sanitizer you use regularly. (Environmental adaptation at work!) Consequently, temporary doses of another algaecide, with which your own personal strain of algae are not acquainted, can help. But regular use of any product promotes development of resistant organisms.

The copper levels above are typical of many ionizer system standards, and also of some copper algaecide products. Controlling copper levels properly -- based on the pools I've seen attempt it -- is no easier than controlling chlorine levels. Overdosing with copper is far more likely to cause long lasting problems than overdosing with chlorine (which is called 'shocking', and is generally recommended!). I have personally seen pools and hair stained green with copper algaecides, and pools stained black and gray with copper from ionizers.


Maintain an appropriate pH:

pH minimum maximum test
All 7.2 7.8 3x week

A pool's pH level affects many things: ideal is usually put at 7.4 - 7.6, and it is often said that chlorine is not effective if the pH gets too high, or even that high pH wastes chlorine. Neither is true, although it is true that you should maintain slightly higher chlorine levels if you pH runs high, than if it runs low. It is also true that a given level of chlorine is more likely to be irritating at a low pH than at a high one. The NSPI manual notwithstanding, there is consensus within most pool publications that it is low pH that contributes to eye irritation, not high pH.

Acid lowers pH; basic or alkaline materials raise pH.


Maintain an appropriate total alkalinity:

alkalinity minimum maximum test
All 60 ppm 120 ppm 2x month

Many people -- including dealers -- get alkalinity and basicity mixed up. A base raises the pH level of water and raises the alkalinity as well. But alkalinity is not simply how basic (or high) the pH is. Rather, alkalinity is a measure of how hard it is to change the pH.

An easy way to imagine it is like this: picture a seesaw. If one end is down, the seesaw is 'acid'. If the other end is down, the pH is 'basic' (or, sometimes 'alkaline'). If the seesaw is easy to move, the seesaw is low in alkalinity. If the seesaw is hard to move, it is high in alkalinity.

Actually, there's a bit more to it than that, but unless you are a chemistry buff, you don't have to get into that bit. The main thing is to have some alkalinity, so your pH won't wander all over the place.

There's a huge amount of controversy about the 'right' way to balance pool water. You'll have to work out levels you and your pool dealer are comfortable with.

Baking soda (sodium bicarbonate) raises carbonate alkalinity; lowering alkalinity is tricky. Simply adding acid, per NSPI guidelines, does NOT work.


Maintain an appropriate calcium hardness level:

calcium minimum maximum test
All 150 ppm 1000 ppm 2x month

Too much calcium and you'll get calcium deposits (usually white or light gray) on the tile at the water line and in your heater, if you have one. You can also end up with cloudy water, though this is not the most common cause of cloudy water.

There's no need to worry about a minimum calcium level in a vinyl pool: the purpose of the calcium is to protect the plaster or Marcite. But the pool powers that be have decreed you should have calcium in all pools -- so JUST DO IT, AND DON'T ASK WHY! After all, they don't know why, and can't give you a straight answer if you do ask.

Calcium is VERY important if have a Marcite or plaster pool and mostly use trichlor for sanitation. Trichlor is acid and will tend to push the pH too low, if you don't watch it. Low pH + low alkalinity + low calcium = high costs replastering your pool!

Adding calcium is easy; getting rid of it is hard. The standard method is to drain and refill. You can also use RO (reverse osmosis) or nanofiltration -- these methods work if you gotta do it and gotta lotta bucks. There's an easy cheap way that works sometimes, and maybe all the time, but it's nonstandard, and does not belong on this page.

Stabilizer (cyanuric acid)

Maintain an appropriate stabilizer level:

stabilizer minimum maximum test
Chlorine* 20 ppm 150 ppm 1x month

The NSPI book says the minimum level is 10 ppm, but I don't know why: none of the test kits will read that low!

Stabilizer is not optional on outdoor pools: the active form of chlorine is quickly destroyed by sunlight. While stabilizer reduces the activity the chlorine present, without it, you will tend to have no chlorine in your pool. Under full sun with clear water in a shallow pool, your chlorine level can go from 5 ppm to 0.1 in three hours! Weak, stabilized chlorine is MUCH better than no chlorine.

However, the more stabilizer in the water, the less active the chlorine you have is. It's not lost or wasted, though. When sun, or goop, consumes the 'active' chlorine, the stabilized chlorine compounds 'release' some of the chlorine, replacing what you just lost.

Of course, none of this applies to PHMB or bromine. PHMB doesn't need stabilizing -- one of its virtues -- and though bromine does, cyanuric acid won't do it. Fortunately, UV (sunlight) destruction is not quite as fast with bromine as with chlorine.

And, you don't need to stabilize indoor pools: there's no sun inside (well, hardly any). Actually, there may be a reason to use small amounts of stabilizer on some indoor pools, but it's far too strange for this page.


Metals minimum maximum test
All 0 ppm 0 ppm3 1x month

The rule about metals is this: if you didn't put them there, they shouldn't be there. Iron (Fe) and copper (Cu) are the usual suspects, when it comes time to point fingers at stains, which come in green, blue, greenish blue, yellow, brown and orange flavors. Manganese (Mn) is fairly uncommon, which is fortunate because it can make a real mess of your pool.

Most dealers seem not to remember to ask homeowners to bring in tap water samples. Troublesome metals in the pool often arrive in the tap water. Well water is very frequently contaminated with metals. Since pools are much more sensitive to metal contaminated water then is your stomach, water that's fine for you may make a mess of your pool. And just because the water analysis at your local treatment plant shows no metals, doesn't mean that you have no metals. A common source of iron and copper contamination are aging water mains.

Although metals can be a problem for all pool owners, those with plaster pools, and particularly with PHMB sanitized pools need to be careful: plaster finishes are more easily stained than pools with painted, fiberglass or vinyl pools. What's more, PHMB is catalytically destroyed by most transition metals, which include just about anything that might be there, and the goo that results can redecorate your pool in a manner even New York raised post-modernists won't appreciate. Each spring, all across the land, poolowners turn their freshly recharged Baquacil pools into an awful mess with the metals straight out of their taps. The Baquacil manual talks about this, but both dealers and homeowners still forget.


TDS minimum maximum test
All 300 ppm 3000 ppm 1x month

I can't help it. This may be the standard chemistry page, but the whole "your TDS is too high" spiel is a crock. Occasionally, TDS may be a useful surrogate marker for a build up of compounds that do cause problems for pools, but in general it means . . . nothing! If your pool is doing OK otherwise, don't let someone with a TDS meter scare you into draining it. For those of you in the pool or aquatics biz, Kent Williams covered the issue pretty well in a recent issue Aquatics Magazine -- it may have been the Jan/Feb '98 issue.


Temperature minimum maximum test
All 78 82 ?

The NSPI's pronouncement that 78 - 82 degrees F. is 'Ideal' is equally nonsense. 'Ideal' for what?

Pool temperature is a difficult and contentious issue. Unlike air temperatures, one degree water temperature changes are IMMEDIATELY detectable by most users. The human body is exquisitely sensitive to relative temperature differences, and in water a one degree shift is enormous.

Architects and engineers: are you listening? Almost all of the pool design books are wrong4, probably because their writers weren't swimmers. It's awfully hard to tell what ideal pool temperature is, when you're wearing a suit and tie!

The bozo promoting the 78 - 82 'ideal' temperature ought to be placed for 30 minutes in a locked dark room with fifteen 70-year-old arthritis class participants after someone readjusts 'their' pool from 88 down to 86.

The best rule I can offer, is this: in hot sun, some people enjoy water temps down to 65 - 70, but not for long. Indoors, almost everyone is miserable below 78, and most folk are unhappy below 84. Above 90 is too hot for almost everyone, except older people with mobility and joint problems. And . . . no matter how cold an 9-year-old boy is, they will stay in the water till they are hypothermic, if they are having fun!


1. Some of the copper/silver systems are apparently EPA approved with only 0.5 ppm of chlorine, half of the level generally recommended. I need to check further on this winter, however. An awful lot of games are being played with 'approvals'!

2. The NSPI 'cheats' on its own standards, here. Because a molecule of bromine is 2.25x heavier than a molecule of chlorine, and because sanitation is a function of the number of sanitizing molecules present, not their weight, it takes 2.25x as many pounds of bromine as it does chlorine, to do the same job. This is not disputed.

Bromine is much more expensive than chlorine, and there is a tendency to 'fudge' the high end requirement for bromine. The NSPI Basic Pool and Spa Technology manual, on page 250, shows chlorine requirements as we have them above. But, they 'fudge' bromine from the proper 2 - 7 ppm (ppm measures the weight of something present, not the number of active sanitizing molecules) and show a range of 2 - 4 ppm, instead. Why? I don't know. But 4 ppm of bromine is equivalent to 1.8 ppm chlorine, NOT 3 ppm chlorine.

It's possible that EPA FIFRA registration label issues are at fault here. The EPA has imposed some upper limits on chlorine levels in pool water that are not based on any science I can find; however the EPA has a history of occasionally making science-free technical judgements, and they may have done so in this case. If so, the manufacturers and NSPI bear less of the blame. On the other hand, the EPA often approves registration labeling based on the data submitted by the manufacturers: if Hydrotech, years ago, submitted bromine at 2 - 4 ppm, then the EPA may not have even investigated higher levels.

3. Surprisingly, given all the money the copper/silver folk pay in NSPI dues, the NSPI manual still says no metals. In this area, I agree completely. Enough copper to kill algae is enough to stain plaster and hair. It doesn't always happen, but it can. This doesn't mean copper is always bad. If your family has dark hair, and you control your copper levels, and don't mind light bluish green stains -- they can actually look pretty nice -- copper away!

4. The whole topic of comfort engineering pools is enormously complicated and apparently poorly understood even by practicing design engineers, judging by all the mis-sized and misapplied HVAC and heating equipment I've seen.

Multiple factors come into play, including the fact that "sensible" heat is NOT the determinant of a wet pool user's comfort level while in the air space! Swimmer and pool user comfort is affected greatly by activity level, personal body fat, body mass to surface ratios, activity and metabolic levels, expectations, mobility, net radiative heat exchange, and multiple other factors. Anyone who tells you that there is an 'ideal' pool temp for multiple types of pool users is merely demonstrating their own ignorance.

The problem is compounded in commercial environments by control strategies currently embedded in the some of the most sophisticated dehumidification systems. Unfortunately, some of these embedded strategies implement some common conceptual errors in hard wired controls or EEPROM stored software.

About Us | Copyrights | Discussion Forum | Subscribe | Sitemap | Write us!