Which chlorine & why?

[stacie_stevens]

At home I use an Aqua Rite Chlorine Generator. This equipment does all the work for me. It was packaged with a chlorine solution already. With this I no longer need to change the chlorine of my pool frequently. For me, this pool equipment is wonderful!

[cburn]

I have a 15x 30 oval and i use the 3 inch tabs, if i was to switch to a liquid what kind of dosing schedule do you normal maintain. i put maybe 2 tabs in every 2 weeks and use 2 gallons every other week to shock it. i have always had clear water and no alge, sometimes i get clody water but i use a clarifier and some FLOC and backwash and it clears up in a day or so. and help would be great

[chem geek]

If you use chlorinating liquid or bleach then you usually have to add it every day or two. If you maintain higher CYA levels and are careful about dosing, then you can add it twice a week or if you don't care about extreme swings in chlorine level then once a week (which is what some pool services do). If you have a pool cover, then twice a week to once a week is much easier since the chlorine demand is much lower (that's what I do in my pool -- twice a week addition).

There are several automation alternatives for dosing including The Liquidator and peristaltic pumps and of course a saltwater chlorine generator. You can learn more by reading the Pool School.

[floridapooltech]

It tends to be preferable to many pool owners to use tri-chlor tablets or sticks as this has everything you would need built in. Using a liquid bleach no matter what the percentage, will dissipate much quicker unless you use cyan-uric acid along with it (stabilizer). Also, with liquid bleach, you will need to add muriatic acid along with it as bleach naturally has a high pH. Not doing so will quickly turn your pools pH too high and you will eventually have balance problems in other areas such as alkalinity, etc...Liquid bleach is fine to use (especially for super-chlorinating purposes), but as you can see, it's more work and less cost effective.

[chem geek]

The bleach or chlorinating liquid will NOT dissipate much quicker if there is already Cyanuric Acid (CYA) in the water. Yes, you should add CYA, but can do so using pure CYA initially. Or one can chlorinate with Dichlor or Trichlor for a while to build up CYA, but then can switch to bleach or chlorinating liquid. It is simply not true that it dissipates faster assuming there is already some CYA added to the water. ALL sources of chlorine produce IDENTICAL chlorine in the water assuming the same water parameters (such as CYA level). Most of the chlorine added to water that already has CYA in it will bind to the CYA while a small amount will remain as hypochlorous acid and hypochlorite ion.

It is also NOT true that bleach and chlorinating liquid lead to rapid and permanently higher pH. Yes, the addition of the products will raise the pH, but chlorine consumption/usage is acidic so the pH drops back down with the net result being close to pH neutral except for the small amount of excess lye -- which is particularly low in 6% Clorox Regular bleach. Technical details about the true pH of chlorine sources is described in this post. I use only 12.5% chlorinating liquid in my pool shown here and here with a daily chlorine usage of around 1 ppm FC (I add it twice a week) and a small amount of acid added every month or two. If chlorine consumption were not acidic, the pH in my pool would rise by 0.3 units per week, but that does not happen as it rises by around 0.1 to 0.2 per month. That's all I add -- about $15 per month in chemical costs for my 16,000 gallon pool. No algaecides, no phosphate removers, no clarifiers, no flocculants, no enzymes, no metal ions, no weekly shocking. There are literally tens of thousands of pool homeowners doing pretty much the same thing using principles originally taught by Ben Powell at The PoolForum and then carried forward at Trouble Free Pool.

You have neglected to tell people the chemical facts that are independent of concentration of product or of pool size as follows:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

So even with a low 1 ppm FC per day chlorine usage, continued use of Trichlor pucks/tabs will increase the CYA level by over 100 ppm in 6 months if there is no water dilution. This happened in my own pool 7 years ago as I have a cartridge filter so no backwashing, live in an area with no summer rains, and had a pump on the cover over the winter putting the water in the sewer and not into the pool (so minimal water dilution). The active chlorine (hypochlorous acid) level that prevents algae growth, kills pathogens and oxidized bather waste is roughly proportional to the FC/CYA ratio so if you don't raise the FC level as the CYA climbs then you can get algae growing faster than chlorine can kill it. This is why it is best to use unstabilized chlorine once the CYA level is at a reasonable level to protect chlorine from degradation from sunlight (usually around 50 ppm, though in very hot sunny areas can be as high as 80 ppm, but should not be higher).

One can operate with Trichlor tabs/pucks and high CYA levels if one pays extra for algaecides or phosphate removers and/or shocks weekly, but this is all extra cost. In fact, when one accounts for the cost of pH adjustment when using Trichlor, it isn't always less expensive than chlorinating liquid or bleach on a per FC basis.

Richard

[Guest]

Very informative! How much Clorox do I add to raise 10,000 gallons 1 ppm? If I know that I can adjust for pool size and ppm target.

Thanks

[chem geek]

It takes 20.7 fluid ounces (about 2.6 cups) of 6% Clorox Regular unscented bleach (6.17% Trade; 5.71% Available Chlorine) in 10,000 gallons to raise the Free Chlorine (FC) level by 1 ppm. You can use The Pool Calculator to calculate dosages for many chemicals and water parameters.

[floridapooltech]

One can operate with Trichlor tabs/pucks and high CYA levels if one pays extra for algaecides or phosphate removers and/or shocks weekly, but this is all extra cost. In fact, when one accounts for the cost of pH adjustment when using Trichlor, it isn't always less expensive than chlorinating liquid or bleach on a per FC basis.

Richard

Chem Geek-

You refer to the use of a phosphate remover as if it were related to CYA levels. This is very untrue. Phosphates are introduced into a swimming pool from fertilizer, areas close to phosphate mines (mainly florida), rain and seawater (then jumping into your pool afterward). Phosphates are algae "food", and therefore have NOTHING to do with CYA. As for algaecides, I use tri-chlor pucks in my own pool, without the need for algaecides. No matter what form of chlorine you use, you will have to superchlorinate using a shock, liquid, etc...This will raise your FC. Stating that the use of tri-chlor tablets will lead to the requirement of expensive phosphate removers, algaecides, flocculants, weekly shocking etc....is false!

[czechmate]

Dear Swimsnaveusa,
Richard has a 1600 inputs mainly water chemistry related. I would venture to say that myself, I never seen him to be of target with his response.
You have to know little more about cross referencing and read between lines to understand, what he refers to.
At CYA 80, just to ward off algae start, you have to maintain FC close to 8ppm. It is expensive and not really healthy to swim in. That is where the starving of potential algae has its true benefit and importance, since even high chlorine presence may not give you needed protection. That starving is achieved by removing phosphates from the water.
Also, believe me, there is a lot more sources of phosphates than you listed here.
Just couple of weeks ago I stopped treating my pool against phosphates coming from pecan pollen. It was totally invisible in the pool water. When I washed patio every morning, the wash-off of was greenish yellow.
We all recognize the phosphates in decaying leaves but the pollen is often invisible culprit, where Phosfree bi-weekly maintenance pays off.
Further, you do not have to superchlorinate on regular basis, as long as you will maintain required level of FC dictated by the CYA level. Only storms and out of ordinary events introducing debris or or organic mater to your pool may require shocking.
To me, removing phosphates is a lot cheaper than trying yo kill established algae with algecides and chlorine shock at 30% CYA.

[chem geek]

Chem Geek-

You refer to the use of a phosphate remover as if it were related to CYA levels. This is very untrue. Phosphates are introduced into a swimming pool from fertilizer, areas close to phosphate mines (mainly florida), rain and seawater (then jumping into your pool afterward). Phosphates are algae "food", and therefore have NOTHING to do with CYA. As for algaecides, I use tri-chlor pucks in my own pool, without the need for algaecides. No matter what form of chlorine you use, you will have to superchlorinate using a shock, liquid, etc...This will raise your FC. Stating that the use of tri-chlor tablets will lead to the requirement of expensive phosphate removers, algaecides, flocculants, weekly shocking etc....is false!

I'm sorry if my post implied the connections that you have referred to. Let me spell this out more clearly. The connection is indirect, not direct.

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases the Cyanuric Acid (CYA) level by 6 ppm. That is a chemical fact. Even at a low 1 ppm FC per day chlorine usage, this is an increase of over 100 ppm CYA in 6 months if there is no water dilution. This is also a fact and happened in my own pool 7 years ago when I was using Trichlor and happens in pool after pool reported on multiple pool forums (including this one). In my pool, it took about 10 months over 1-1/2 swim seasons at around 0.8 ppm FC per day to go from 30 ppm to over 150 ppm CYA -- I have a cartridge filter so no backwashing and there are no summer rains and I had a pool cover pump for the winter on my electric safety cover so essentially minimal dilution of the pool water. Even though I was using a PolyQuat algaecide, though only every other week, after I got to 150 ppm CYA the chlorine demand in my pool shot up and it was harder and harder to keep up with chlorine demand until eventually the water started to turn dull and then cloudy as algae grew more and more quickly. That's when I decided to learn pool water chemistry to figure out what was going on in my pool and quickly learned about the chlorine/CYA relationship (from both scientific literature and from The PoolForum.

Higher CYA levels require proportionately higher FC levels to have the same active chlorine (hypochlorous acid) level. This is also a chemical fact known since at least 1974 as determined from the equilibrium constants in this scientific paper and that describe in further detail in this post. It is the hypochlorous acid that is largely responsible for disinfection, oxidation and prevention of algae growth. So as the CYA level climbs from continued use of stabilized chlorine products, the FC must be proportionately raised if one is to prevent algae growth without the use of supplements (unless one is lucky with nutrient-poor water).

Algae are plants and need water, sunlight, a source of carbon (such as carbonates and carbon dioxide), a source of nitrogen (such as nitrates or for some cyanobacteria aka blue-green algae, nitrogen gas), and a source of phosphorous (such as orthophosphate or, more slowly taken in, simple organic phosphates). Algae growth is also dependent on temperature.

So there is a race between algae growth which is limited by the above factors vs. the rate of killing by chlorine which is based mostly on the hypochlorous acid concentration which in turn is proportional to the FC/CYA ratio. Even with all of the phosphate and nitrate nutrients that algae could possibly utilize, their growth is still ultimately limited by sunlight and temperature where algae doubles in population in 3 to 8 hours depending on species. Therefore, chlorine is able to kill algae faster than it can reproduce if the FC/CYA ratio is high enough. For almost all green algae found in pools, having the FC be at least 4.5% of the CYA level kills the algae faster than it can grow and is suitable as a minimum chlorine level for saltwater chlorine generator (SWG) pools. In manually dosed pools, the recommendation is usually 7.5% of the CYA level.

If one does not maintain the minimum FC/CYA ratio (including cheating if one shocks regularly), then one can supplement the chlorine in preventing algae growth by either using an algaecide (PolyQuat 60, copper ions, 50 ppm borates, etc.) or use a phosphate remover to slow down algae growth. If one happens to have a pool poor in phosphates, then obviously the phosphate remover isn't necessary.

If one maintains chlorine at the appropriate FC/CYA levels, then there is no need for shocking the pool. The chlorine is able to keep up with oxidizing bather waste, killing pathogens, and preventing algae growth continually so there is no need to raise the FC on a regular basis. See this thread to see that the tens of thousands of pool users at The PoolForum and Trouble Free Pool do not need to shock their pools except for infrequent circumstances such as pool openings, dead animals, etc. Why do you believe that shocking a pool to raise the FC is necessary?

As for your own pool, you are fortunate that your continued use of Trichlor has not led to unusually high chlorine demand or algae growth. Your regular shocking helps make up for the low FC/CYA ratio and you may have more water dilution in your pool from backwashing or rain overflow that keeps your CYA from rising too quickly. Your pool might be naturally low in algae nutrients including nitrates or phosphates. You might even be using Trichlor that has copper in it (some does). My fill water contains 400 ppb phosphates and my pool has had 2000-3000 ppb phosphates yet did not get algae (after that first year) so long as I kept the proper FC/CYA ratio just as the tens of thousands of residential pool owners have done.

The pool store where I buy my chlorinating liquid also services thousands of pools (they have many trucks and personnel) and they make sure the CYA level doesn't get above 100 ppm and they keep a minimum 4.5 ppm FC level in those pools. I asked them why and they said it was to prevent algae growth, that the manufacturers told them there was no problem to 200 ppm CYA, but the pool store folks said that simply wasn't true in their experience. They also found that the 1-3 ppm FC recommendation from BioGuard and the 1-1.5 ppm recommendation from GLB were woefully inadequate at the higher CYA levels.

But most importantly, it is the tens of thousands of pool owners that have validated that chlorine alone can be used to prevent algae with no need for regular shocking or supplemental products and also having a stable pH (which cannot be said for Trichlor which requires pH raising products since it is so acidic). The most common reason by far for algae problems reported on multiple pool forums is from too low an FC/CYA ratio which usually comes about from continued use of stabilized chlorine products (Trichlor and Dichlor) that continually raise the CYA level. When the science is there and people's experience validates it on a large scale, it seems pretty solid to me.

Trichlor ---> CYA increases ---> FC/CYA decreases ---> HOCl decreases ---> Algae grows faster than chlorine can kill it
Phosphate Remover ---> Phosphates decrease ---> Algae grows slower so lower chlorine can kill it

Richard

[brianVLX]

I'm wanting to switch from Trichlor to Liquid Chlorine. I have a 30,000gal above ground pool. How do I determine how much liquid chlorine to dump in? And do I do this daily?? Any tips or info would be appreciated!

thanks,
Brian

[chem geek]

You can use The Pool Calculator to calculate dosages. If you don't use a partially opaque (say, blue as opposed to clear) pool cover, then you will need to add chlorine every day or two. I have a mostly opaque cover and add it twice a week. You can add it less frequently if you have more chlorine swings or you can automate chlorine dosing using The Liquidator or a peristaltic pump or a saltwater chlorine generator.

You can use the Trichlor tabs/pucks when you go on vacation (for about a week) and can use them occasionally if your CYA gets low from water dilution. You can use Cal-Hypo when you want to raise your Calcium Hardness (CH). Read the Pool School for more info on how to maintain your pool.

A 30,000 gallon pool is rather large so the chlorine quantities will be high unless you use a pool cover that is at least partially opaque to the UV rays in sunlight. You can reduce chlorine loss from sunlight with a higher CYA level, but that gets risky if the FC gets low. The main point is to learn about your options and the effects of different chlorine sources and figure out what works best for you.

[brianvlx]

Thanks for the input! Here is another for you....what's your opinion on "The Liquidator"???? I've tried to search for some reviews, etc...but haven't found much useful info other than how it works (which i found on the company's website). Do they work? Any issues with them? Costs? Where do you get them?

Any input would be appreciated!!

[chem geek]

It works for some people but not for everyone. You can read more about it at this thread, this thread and this thread.

There is an upgrade to the tubing in both quality and size (1/2" to 3/8") that is essential and unfortunately you have to do yourself. To minimize the amount of calcium deposits in the output valve, one can use 50 ppm Borates, keep the saturation index slightly negative, and/or use 6% bleach instead of 10%/12.5% chlorinating liquid. However, some of those using the Borates have been able to use chlorinating liquid. Also, get the 8-gallon unit.

The Liquidator is sold here for around $180. You can see an instruction manual here.

[PBROWN]

Liquid Chlorine is a great time proven method of sanitization.
There can be complications in hauling, and leaking.
Sticks are kept in an air tight drum which reduces corrosion
in the pump room. Less trouble to haul for the average pool owner.
Plus, they are already stabilized. But Soda Ash will have to be added
on a regular basis for pH balance.

Thanks,
Pat Brown