The PoolSolutions Best Guess Swimming Pool Chlorine Chart

What's a "Best Guess Swimming Pool Chlorine Chart"?
Most of the published guides to correct swimming pool chlorine levels, from the NSPI, the CDC, the NSPF, etc. are often unhelpful and sometimes just plain wrong. The "Best Guess Chart" has proved to be a valid and useful correction.

Hey, I don't need a long explanation -- where's the chlorine chart?
Here! -- just click this link to jump to the chart!

Why a "best guess" guide to pool chlorine levels?
When I first published this chart, sometime before 2004, I was pretty sure my approach to adjusting swimming pool chlorine levels according to stabilizer levels was valid.
When I created the first "Best Guess Chart", a number of years ago, it was just that, my "guess" based on my own experiences with commercial pools, a lot of experience by Pool Forum users, a little known technical paper by John Wojitowicz (retired from Olin Chemicals), and a little math. But, I no longer had the math skills to use the equations from some scientific papers I had, so I could not actually calculate the exact adjustments. Also, from 20 years of helping different organizations manage large commercial pools, I knew that there were some practical factors that the equations didn't consider.

So, I made 'educated' guesses -- hence, the name "Best Guess". My guesses proved to be good ones -- not perfect, but much better than the 'standard' guides to chlorine doses found in the official literature from the NSPI, NSPF, and CDC.

Since that time Richard "Chem_Geek" F. has done some really important work, published on the Pool Forum and elsewhere that does use those equations. And, he's helped develop a more exact, but (in my opinion) a somewhat more confusing set of tables. The updated tables below reflect both some of his work, and my opinion that simpler is sometimes better. For example, it's not clear that the "bleaching" effects of chlorine, on suits, skin and hair, are identical with the FAC chlorine levels. The red zones above reflect my own experience in observed swimwear damage in highly stabilized pools. But both of us agree that more study and work is needed.

How does it work?
What I suspected and had seen in my own pool operation experience; what John Wojitowicz argued in papers published some years ago in the Journal of the Swimming Pool Industry; and what "Chem_Geek"  has analyzed at length is actually a fairly simple idea:as stabilizer levels go up, chlorine levels need to go up as well.

Well, why not just run LOW chlorine levels without stabilizer?
On indoor pools, with no exposure to sunlight, that's definitely an option.

But on outdoor pools, chlorine's half-life without stabilizer can be as little as 30 minutes under full so. This means that if you have 1 ppm at noon, you'll have 0.5 ppm at 12:30 and 0.25 ppm. To keep a pool safe under those conditions means that you have (1) add chlorine continuously, and (2) have a really good circulation system that is running 24/7.

It also turns out you have to be willing to use a lot more chlorine than you would otherwise.

So stabilizer is necessary for good sanitation?

Without stabilizer, everything has to be pretty much perfect in order to maintain a santized and algae free pool. Years ago, commercial pool were operated with chlorine gas, soda ash, and not much more. There were a lot of cloudy, stinky public pools!

Swimming pools are enough work, even when done right. The BBB Method is ALL about not making it worse by adding stuff you don't need.
Well, the chart let's me figure my chlorine level, if I know what my stabilizer level is. But what are the BEST levels?
I don't think there is one. As long as you have enough chlorine to go with your stabilizer, any of the levels listed will work. However, unless you want to test your pool 2x per day, you'll probably want to maintain stabilizer levels above 40 ppm.

I've been using chlorine tabs for years, and now my stabilizer level is over 200 ppm, and my dealer says I have "chlorine lock" and have to drain and refill my pool. Is that correct?
No, "clorine lock" is a pool industry term that reflects the fact that most dealers and even most pool chemical manufacturers don't understand how chlorine and stabilizer work together.

It's true, that you can't run standard chlorine levels successfully -- you'll need to adjust your chlorine levels to compensate. And, that means you'll need a drop-count chlorine test kit.

Would it just be easier to drain and refill?
Actually, it would probably be easier to adjust your levels and use the drop-count testkit

A really large pool service company in the Southwest (PoolClor) has been taking care of home pools for more than 40 years, using a method that is explained by this chart. They adjust their customer pools to have stabilizer levels over 100 ppm, and treat them with weekly injections of chlorine gas.

Some of them eventually figure it out . . . and become dishonest. Some of them put their heads in the sand. But quite a few still believe.

So, while you can't trust them . . . they are necessarily lying to you deliberately.

What about the swimming pool chemical manufacturers -- are they dishonest?
I can't answer that question without saying things that will get me in trouble.

But, I can point out that "Chem_Geek", a regular on the PoolForum and elsewhere, has taking the practical proof I had of my methods, and built a comprehensive and very technical chemical explanation of how and why. He's worked very, very hard to try to persuade the NSPF, various state code bodies, and others to correct the published errors. He's gotten some pretty nasty bruises banging his head on those walls. You can check out some of that in the "China Shop" on the Pool Forum, if you like

Aren't you afraid to say some of this stuff?
I used to be.

When PoolSolutions first started, when I looked in my webserver logs, I'd see BioLab's IP tracks crawling all over the site -- they were VERY familiar with what I was publishing. Long before the BBB method ever was called that, I realized that wide publication of the material here could hurt BioGuard, Robarb, HTH Chemicals and others a lot. I figured that every dollar I made selling information cost the pool chemical business $100, $200 or more.

I knew that I would win any lawsuit, if I could afford to pay expensive attorneys to defend me. But I couldn't. So, any of the big companies could have taken me out simply by filing a bogus lawsuit against me: they would have won, simply because I couldn't afford to fight back. My only hope would have been if I could get some "David versus Goliath" press coverage -- and I actually made preparations to do just that.

But several things have changed.

There are now at least two OTHER forums operating with the information first published here. Also, many pool service tech use at least some of the info here. And Chem_Geek's technical analysis makes it much hard to dismiss some of my criticisms as merely malicious speculation. So do the 50,000 or 100,000 pool owners actually USING these methods.

But, another fact is in play, as well. SWCG (salt water chlorine generators) are gradually eating the pool chemical manufacturer's lunch. I know, they know, and the generator manufacturers know that the pool chemical biz is going to shrink a lot over the next 20 years, with or without me. So, what I write here is not nearly the threat it used to be, nor would it be as easy to slap down.

Ben's Best Guess* Guide to Swimming Pool Chlorine
version 2.0

Free chlorine (FC) ppm levels Notes
Min Max 'Shock' +Shock+
0 - 10 1 3 10 15 Caution: at these stabilizer levels, in outdoor pools in full sun, FC levels in the yellow ranges can disappear  in minutes.
10 - 20 2 5 12 20 Caution: orange levels are generally harmless to naked  swimmers, but can be quite damaging to swim suits. True competition suits, all polyester or all nylon suits are resistant. Very expensive fashion suits are NOT resistant!
30 - 50 3 6 15 30
60 - 90 5 10 20 75 Caution: red levels are can be irritating to skin, can
damage hair, lighten pool liners and are very damaging to swimwear. Additionally, at these stabilizer levels, chlorine will drop VERY slowly. This can make the pool unusable  for a long period.
100 - 200 8 15 25 100

There are several important points to consider in using this chart.

First: The levels above assume that you are testing water from a well-circulated pool, with a decent flow distribution. Most home pools with pumps running on high meet this requirement. But if your pump has been off, or if you are testing water from a typical suburban community pool, you need to collect several samples and test them.

Second: While this is -- to the best of my knowledge -- a 'no-harm' chart to people, the no-harm applies to naked people with normal skin. People with sensitive skin may experience significant skin irritation at the higher chlorine levels, and swim suits containing Lycra will be damaged. Also, people with dyed or treated hair are MUCH more likely to experience adverse effects And while all polyester or nylon suits may not be damaged physically, they are likely to be bleached. All these effects, except maybe those to sensitive skin, are time based. A brief dip in a pool at FC=50 and CYA=60 probably won't lighten undyed hair, but a user swimming laps daily probably will see effects.

Third: many of the chemical levels shown here are difficult to field test. Even with DPD-FAS, chlorine levels above 50 ppm are hard to measure, and it's easy to screw up testing. CYA levels below 20 or above 100 are also difficult to measure with the kits available to pool  users. There are some clumsy work-arounds, but they are not ideal. SO, for some levels, testing has to be replaced by 'dead reckoning'. I can't test for 5 ppm of stabilizer, but if I add 5# to the skimmer of a freshly filled 120,000 gallon community pool, with a freshly backwashed sand filter, I can pretty much 'reckon' on 5 ppm of CYA when I return a day later. 

Ben's Best Guess Guide to Swimming Pool Chlorine - ver. 2.0 - 16 Aug 2010
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Ben Powell -- All Right Reserved.

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