Pool Water Analysis

[robertsonmartin]

Hi All,

I'm up to speed with the theory of balancing the pool water, what the correct levels should be, how to treat it etc but have a little query.

My pool has a Compupool CPSC series salt chlorinator system so I don't manually add any chlorine medium. The chlorine level in the water is always pretty good hanging around the 2.8 to 3.0 ppm level. The pH level rises slowly over the course of approx 10 days from 7.2 to 7.7 when I will then add a couple of litres of HCl which brings it back down to 7.2 and the the cycle starts again. This apparently is normal for a salt chlorinator system for the pH to balance out at pH 7.8 according to my chlorinator manual *.

Now, the Total Alkilinity, is a strange one. It will normally hang around the 60ppm limit which I know is well below the 100 - 120ppm level that it should be if I do nothing to it at all. If I add Sodium Bicarb to bring it up to the correct level of 120ppm, this throws out the pH a little and then I need to add HCl to bring this back down to 7.2. This in turn affects the TA level by reducing it by 20ppm. The TA then gradually drops over the course of about 2-3 weeks from 100ppm back down to 60ppm.

Water hardness levels are fine, and the pool water always look sparkling clean. Water temp approx 28.5 - 30 degC.

I have read that as long as the chlorine and pH levels are stable (they are in my case) there isn't much point in messing around with the TA and that I should just leave this one alone at 60ppm. If the TA is brought up to 100ppm this doesn't stop the pH from slowly rising.

Any comments?

M.

* Chlorinator manual states - pH produced by the Chlorinator is close to neutral pH. However, other factors usually cause the pH of the pool water to rise. Therefore, the pH in a pool chlorinated by thr Chlorinator tends to stabilize at 7.8. This is within national standards. If the pool pH rises above 7.8 have a pool professional test to see if other factors such as high Calcium Hardness or Total Alkilinity are the cause and then balance accordingly.

[fdimike]

I believe the best way to approach this is as follows:

1. Adsjust the total alkalinity first (acts a a buffer to prevent rapid changes in Ph)

2. Adjust the level of Stabilizer (Cyanauric Acid)

3. Adjust the Ph

The cyanauric acid will bring down the Ph a bit. If you are not using this cycnauric acid you should as it slows down the loss of FREE Chlorine in the pool dramatically. The sun here in LOS will disipate the FREE CHLORINE quite rapidly without it. I bought a large drum of it from the Pool Dr. at a very reasonable price (much cheaper than buying small containers of Stabilizer). Make sure your test kit measures FREE CHLORINE and not just TOTAL CHLORINE. The FREE CHLORINE is what acts as the sanitizer in a swimming pool.

I hope this helps.

[sometime]

I thought that in a pool using a salt chlorinator all the chlorine was FREE and not TOTAL because when the chlorine has done its job and killed any bacteria etc etc it turns back into salt to continue the process.

I believe the best way to approach this is as follows:

1. Adsjust the total alkalinity first (acts a a buffer to prevent rapid changes in Ph)

2. Adjust the level of Stabilizer (Cyanauric Acid)

3. Adjust the Ph

The cyanauric acid will bring down the Ph a bit. If you are not using this cycnauric acid you should as it slows down the loss of FREE Chlorine in the pool dramatically. The sun here in LOS will disipate the FREE CHLORINE quite rapidly without it. I bought a large drum of it from the Pool Dr. at a very reasonable price (much cheaper than buying small containers of Stabilizer). Make sure your test kit measures FREE CHLORINE and not just TOTAL CHLORINE. The FREE CHLORINE is what acts as the sanitizer in a swimming pool.

I hope this helps.

[fdimike]

I have a slat water pool with 2 Poolrite Chlorinators. I measure both free and total chlorine in the water. It's my understanding that some of the free chlorine combines with other elements/pollutants in the water to create the total chlorine which is essentially of no use.

[fdimike]

I think I made a mistake in the order of doing things in my earlier post. I think you should adjust the Total Alkalinity first followed by the Ph and then the Cyanauric acid. The pool water should be correctly in balance before checking the level of Cyanauric Acid (stabilizer). The Cyanauric Acid should not effect the Ph very much at all.

My apologies.

[robertsonmartin]

I think I made a mistake in the order of doing things in my earlier post. I think you should adjust the Total Alkalinity first followed by the Ph and then the Cyanauric acid. The pool water should be correctly in balance before checking the level of Cyanauric Acid (stabilizer). The Cyanauric Acid should not effect the Ph very much at all.

My apologies.

Thanks for your help. I forgot to mention in my original post that the pool has cyanuric acid in it, this level only really changes (falls) if there is heavy rain and the overflow tank overflows to drain. My pool test kit tests for free chlorine.(DPD type). I think what I'll do is adjust the TA back up to 120ppm, balance pH as you say and then see how long it takes again for the pH to climb back up to 7.7 and compare it to how long it took with the TA down at 60ppm.

The pool doesn't get much use except for myself swimming in it daily for an hour and we haven't had any rain to speak of for a couple of weeks so I should be able to get a good comparison.

Cheers.

[fdimike]

Robert

My pool doesn't get much regular use other than from myself. My relatives enjoy the water as well but not as frequently. In any event my Ph also creeps up. The speed of the "creep" is really dependant on the water source. Rain water which we have had buckets of this year causes a slower upward climb than city water which I use to maintain the water level in the dry season. I also use a small amount of HCL to bring the Ph back down. If your TA is where it belongs the changes in Ph should be relatively minor and easy to manage.

BTW: I don't know where you buy your sodium bicarb but I have been using 2 lb boxes of Arm & Hammer brand. It is readily available here in udon Thani @ 55B/2lb box which is cheaper for me than buying it from a pool supply company.

Best of luck

[robertsonmartin]

Robert

My pool doesn't get much regular use other than from myself. My relatives enjoy the water as well but not as frequently. In any event my Ph also creeps up. The speed of the "creep" is really dependant on the water source. Rain water which we have had buckets of this year causes a slower upward climb than city water which I use to maintain the water level in the dry season. I also use a small amount of HCL to bring the Ph back down. If your TA is where it belongs the changes in Ph should be relatively minor and easy to manage.

BTW: I don't know where you buy your sodium bicarb but I have been using 2 lb boxes of Arm & Hammer brand. It is readily available here in udon Thani @ 55B/2lb box which is cheaper for me than buying it from a pool supply company.

Best of luck

I get 25Kg bags of Sodium Bicarb here for 650baht. I brought the TA up this morning back to 110ppm by adding 5Kg. pH is still in tolerance so will keep an eye on it.

[WarpSpeed]

I believe the best way to approach this is as follows:

1. Adsjust the total alkalinity first (acts a a buffer to prevent rapid changes in Ph)

2. Adjust the level of Stabilizer (Cyanauric Acid)

3. Adjust the Ph

The cyanauric acid will bring down the Ph a bit. If you are not using this cycnauric acid you should as it slows down the loss of FREE Chlorine in the pool dramatically. The sun here in LOS will disipate the FREE CHLORINE quite rapidly without it. I bought a large drum of it from the Pool Dr. at a very reasonable price (much cheaper than buying small containers of Stabilizer). Make sure your test kit measures FREE CHLORINE and not just TOTAL CHLORINE. The FREE CHLORINE is what acts as the sanitizer in a swimming pool.

I hope this helps.

Very good Mike but a couple of additional items..

1) The stated Ph is too low on all accounts, 7.6 is ideal and anything lower then 7.5 becomes quite corrosive to the entire system which includes your chlorinator cells..

Secondly proper application of acid is key here as to adjust Ph levels you distribute the acid over a wide area and to adjust T/A you pour it in one location such as in front of a flowing return but not if that return is pointing towards your wall as it will erode your surface over time or in the deep end. By pouring it in one location you completely 'wash out' the alkalinity in that area and as that diluted 'washed out' water distributes it blends with the rest of the pool volume & brings down the T/A levels throughout the pool, then recheck in about 2 to 3 days to see what result you have..

Adjusting the T/A will most definitely effect the Ph dramatically which you will then need to re-adjust to proper levels but not conversely if done this way, but over time you will still have to make adjustments due to other natural and human factors..

[WarpSpeed]

I thought that in a pool using a salt chlorinator all the chlorine was FREE and not TOTAL because when the chlorine has done its job and killed any bacteria etc etc it turns back into salt to continue the process.

I believe the best way to approach this is as follows:

1. Adsjust the total alkalinity first (acts a a buffer to prevent rapid changes in Ph)

2. Adjust the level of Stabilizer (Cyanauric Acid)

3. Adjust the Ph

The cyanauric acid will bring down the Ph a bit. If you are not using this cycnauric acid you should as it slows down the loss of FREE Chlorine in the pool dramatically. The sun here in LOS will disipate the FREE CHLORINE quite rapidly without it. I bought a large drum of it from the Pool Dr. at a very reasonable price (much cheaper than buying small containers of Stabilizer). Make sure your test kit measures FREE CHLORINE and not just TOTAL CHLORINE. The FREE CHLORINE is what acts as the sanitizer in a swimming pool.

I hope this helps.

Nope, the salt is salt, the Cl2 is Cl2, but does contain some minimal salt residue but still has nothing to do with combined Cl2 versus free active....

[WarpSpeed]

I think I made a mistake in the order of doing things in my earlier post. I think you should adjust the Total Alkalinity first followed by the Ph and then the Cyanauric acid. The pool water should be correctly in balance before checking the level of Cyanauric Acid (stabilizer). The Cyanauric Acid should not effect the Ph very much at all.

My apologies.

Yes I catch that now too, adjust the CYA afterwards as high Ph and T/A reduce it's effectiveness but it effects the Ph and T/A negligibly..

[robertsonmartin]

I believe the best way to approach this is as follows:

1. Adsjust the total alkalinity first (acts a a buffer to prevent rapid changes in Ph)

2. Adjust the level of Stabilizer (Cyanauric Acid)

3. Adjust the Ph

The cyanauric acid will bring down the Ph a bit. If you are not using this cycnauric acid you should as it slows down the loss of FREE Chlorine in the pool dramatically. The sun here in LOS will disipate the FREE CHLORINE quite rapidly without it. I bought a large drum of it from the Pool Dr. at a very reasonable price (much cheaper than buying small containers of Stabilizer). Make sure your test kit measures FREE CHLORINE and not just TOTAL CHLORINE. The FREE CHLORINE is what acts as the sanitizer in a swimming pool.

I hope this helps.

Very good Mike but a couple of additional items..

1) The stated Ph is too low on all accounts, 7.6 is ideal and anything lower then 7.5 becomes quite corrosive to the entire system which includes your chlorinator cells..

Secondly proper application of acid is key here as to adjust Ph levels you distribute the acid over a wide area and to adjust T/A you pour it in one location such as in front of a flowing return but not if that return is pointing towards your wall as it will erode your surface over time or in the deep end. By pouring it in one location you completely 'wash out' the alkalinity in that area and as that diluted 'washed out' water distributes it blends with the rest of the pool volume & brings down the T/A levels throughout the pool, then recheck in about 2 to 3 days to see what result you have..

Adjusting the T/A will most definitely effect the Ph dramatically which you will then need to re-adjust to proper levels but not conversely if done this way, but over time you will still have to make adjustments due to other natural and human factors..

Hi Warpspeed,

Thanks for your advice, it is appreciated. you mention pH 7.6 is ideal and anything less is corrosive, but the various book and manuals i have read regarding pool maintenance generally state that the ideal pH is 7.2 to 7.6. With fresh water pH being 7.0, eyes are 7.4 etc. and chlorine effectiveness drops off with a pH greater than 7.6.

Actually maintaining the pool at 7.6 becomes much easier for me as it normally hangs out at this level anyway. Good information on where to add the Bicarb when raising the TA.

Cheers.

M.

.

[WarpSpeed]

I believe the best way to approach this is as follows:

1. Adsjust the total alkalinity first (acts a a buffer to prevent rapid changes in Ph)

2. Adjust the level of Stabilizer (Cyanauric Acid)

3. Adjust the Ph

The cyanauric acid will bring down the Ph a bit. If you are not using this cycnauric acid you should as it slows down the loss of FREE Chlorine in the pool dramatically. The sun here in LOS will disipate the FREE CHLORINE quite rapidly without it. I bought a large drum of it from the Pool Dr. at a very reasonable price (much cheaper than buying small containers of Stabilizer). Make sure your test kit measures FREE CHLORINE and not just TOTAL CHLORINE. The FREE CHLORINE is what acts as the sanitizer in a swimming pool.

I hope this helps.

Very good Mike but a couple of additional items..

1) The stated Ph is too low on all accounts, 7.6 is ideal and anything lower then 7.5 becomes quite corrosive to the entire system which includes your chlorinator cells..

Secondly proper application of acid is key here as to adjust Ph levels you distribute the acid over a wide area and to adjust T/A you pour it in one location such as in front of a flowing return but not if that return is pointing towards your wall as it will erode your surface over time or in the deep end. By pouring it in one location you completely 'wash out' the alkalinity in that area and as that diluted 'washed out' water distributes it blends with the rest of the pool volume & brings down the T/A levels throughout the pool, then recheck in about 2 to 3 days to see what result you have..

Adjusting the T/A will most definitely effect the Ph dramatically which you will then need to re-adjust to proper levels but not conversely if done this way, but over time you will still have to make adjustments due to other natural and human factors..

Hi Warpspeed,

Thanks for your advice, it is appreciated. you mention pH 7.6 is ideal and anything less is corrosive, but the various book and manuals i have read regarding pool maintenance generally state that the ideal pH is 7.2 to 7.6. With fresh water pH being 7.0, eyes are 7.4 etc. and chlorine effectiveness drops off with a pH greater than 7.6.

Actually maintaining the pool at 7.6 becomes much easier for me as it normally hangs out at this level anyway. Good information on where to add the Bicarb when raising the TA.

Cheers.

M.

.

Yes they say that, yes there is truth in that, as I said, it is "ideal".. Corrosiveness increases greatly below that mark but it's not too serious and eyes are not the only consideration, skin is too, so that's why 7.6 is the ideal compromise to balance between human comfort, Cl2 effectiveness and equipment durability and yes lower Ph levels is better for Cl2 effectiveness.. So for swimmer comfort, equipment durability, ease of maintenance and Cl2 effectiveness throw out anything lower then 7.5 and be very diligent to keep it above that mark. To do that your T/A readings are critical as they provide that stability in your Ph so that it doesn't fluctuate as you're describing. If it does, it's a red flag that your T/A is low and needs adjusting, T/A is constantly under attack by salt chlorinators and acid rain which is also common here..

Back where I come from it's converse as the rain is very high in alkalinity due to the addition of more liquid Cl2 which is basic in nature and rain water primarily coming from what is called Coquina which is crushed up seas shells and is lime based so adding acid is constant but much easier to maintain then always adding Bicarb..

Bicarb distribution is not so complicated just dilute it in a bucket and distribute it across the pool..

One more thing, you don't use Bicarb to adjust your Ph when it's low you use soda ash (baking powder not baking soda) and it will not effect your T/A measurably. Bicarb is for T/A adjustments and soda ash is for Ph adjustments (if you need to bring it up) once your T/A is at proper levels but only after the T/A is stable and given a few days to fully effect the pools chemistry..

You can put your hand in the bucket while mixing the bicarb and the temp actually drops significantly from the chem reaction. I used to do this in the heat of the summer and put both my hands in to get some heat relief, it really works as it cools your wrists where your arteries are but DO NOT do this with soda ash!! It is very reactive and does the exact opposite and will BURN your hands!! Use something to stir the soda ash with and then distribute across the pools surface..

Edited August 17, 2011 by WarpSpeed

[Naam]

Yes they say that, yes there is truth in that, as I said, it is "ideal".. Corrosiveness increases greatly below that mark but it's not too serious and eyes are not the only consideration, skin is too, so that's why 7.6 is the ideal compromise to balance between human comfort...

i beg to differ WarpSpeed. a pH of 7.0 is absolute neutral and not corrosive. actual corrosiveness starts at 7.5 and above and 6.5 and below. the pH of the human skin surface varies between 6 and 6.5, in some cases down to 5 or even below (and that with perfectly healthy people!).

Normal skin surface pH is between 4 and 6.5 in healthy people, though it varies among the different areas of the skin.

http://mobilenursing.blogspot.com/2009/02/use-of-soap-on-skin-of-sick-and-elderly.html

the often mentioned "ideal" 7.2 are based on the average pH of human eye fluid. the jury is still out which of the schools advocating a pH below and above 7 are right. most probably they will always agree to disagree. based on the comfort of Mrs Naam and her skin, who uses the pool daily, i kept my pools since many years at 6.5 because she claims that's perfect for her and does not require any body lotion after completing her 120 laps.

[WarpSpeed]

Yes they say that, yes there is truth in that, as I said, it is "ideal".. Corrosiveness increases greatly below that mark but it's not too serious and eyes are not the only consideration, skin is too, so that's why 7.6 is the ideal compromise to balance between human comfort...

i beg to differ WarpSpeed. a pH of 7.0 is absolute neutral and not corrosive. actual corrosiveness starts at 7.5 and above and 6.5 and below. the pH of the human skin surface varies between 6 and 6.5, in some cases down to 5 or even below (and that with perfectly healthy people!).

Normal skin surface pH is between 4 and 6.5 in healthy people, though it varies among the different areas of the skin.

http://mobilenursing.blogspot.com/2009/02/use-of-soap-on-skin-of-sick-and-elderly.html

the often mentioned "ideal" 7.2 are based on the average pH of human eye fluid. the jury is still out which of the schools advocating a pH below and above 7 are right. most probably they will always agree to disagree. based on the comfort of Mrs Naam and her skin, who uses the pool daily, i kept my pools since many years at 6.5 because she claims that's perfect for her and does not require any body lotion after completing her 120 laps.

Perfect for HER but not perfect, and especially for the rest of your pool and from what you've said there's room for adjustment to bring it up and still make it comfortable for her. Your're not differing with me Naam, you're differing with decades of successful pool chemistry. As for "neutral" that all depends on the make up of the various mechanicals in a given pool system everything from alkaline based cements to various plastics and metals of varying compounds that all react differently to different pH levels regardless of whether 7.0 is neutral on the Ph scale or not so a compromise has to be reached with swimmer comfort, sanitation and equipment longevity this led to the compromise of 7.6 Ph to accommodate all of these various factors.

If for example you run your pool as low as you've mentioned for human comfort then you now reduce the longevity of pool surfaces and equipment. Back when, where you come from the most common pool surface was Marcite until laws removed asbestos as the catalyst which made it substantially softer and shortlived and it was very basic and lime based as is the more recent products like Diamond bright or Pebble tech so a Ph that low would knock years off of the life expectancy of those surfaces which is quite expensive to replace.. Now in Thailand it's actually even worse, as you think tile holds up better but the catalyst that holds the tile on the pool and seals it being the grout and mortar is very soft and in small proportions and won't hold up well to anything close to that Ph. Once the grout is gone the mortar is then attacked and soon you have a leaking pool with tile falling off..It's a compromise as I said.. Most metals used in pumps and internal parts also don't hold up well to Ph levels that low and plastics, especially cycolac become brittle...

Ph does not work alone it works in 'balance' with T/A and the problem with Ph levels that low is that it multiplies the effect of Cl2 10 fold (estimate depending on many factors the largest one being the T/A) and therefore IT becomes both more corrosive/errosive and more uncomfortable for swimmers. This is often misunderstood as people often tag the Cl2 being too high as the problem for blonde hair turning green, blood shot eyes or dry skin when it is the reaction and increased strength of the Cl2 due to the low levels of the Ph and that other little understood culprit being T/A.

These chems do a tight rope balancing act (hence the term water balance) and work in concert with each other when at the correctly stated levels but I've seen pools with nearly 0 free active Cl2 that were causing all of these symptoms due to low Ph and T/A not high Cl2 but because they raised the Cl2 level effect so high.. Conversely I've seen numerous pools at levels like 6-10PPm and not a single complaint because the Ph was in balance and was up around 7.7 to 7.8 but then a lower T/A is in order to keep the pool from either crystallizing or calcifying...

I typically kept my pools at an 80 to 110 T/A and at minimum a 4-6 PPm Cl2 level with a 7.5 to 7.8 PH one once a week service and no salt chlorinators and never had issues, more over hundreds of satisfied pool owners but still like all women all pool water is not the same nor are all swimming pools they all have their quirks and a good tech needs to adjust for the conditions of each one accordingly..

Here's a quote from a North Carolina State website so you won't have to take my word for it:

And the informative link: Water chemistry

In pools a slightly alkaline pH of 7.4 to 7.6 is most desirable because this range is most comfortable to the human eye and provides for optimum use of free chlorine while maintaining water that is not corrosive or scale forming.

This is also why those water chemistry computers you and I are so familiar with will NEVER replace a first rate tech as they are only a sales tool and can not read the real situation with a pool while in a store. I remember one case where I had to save a guys pool that was seriously calcifying while the pool store was still prescribing more Ca because his levels were too low. The problem was once I found out how much they had already prescribed and sold him along with his symptoms of a cloudy rough pool, alarms went off immediately and yes as it turned out his pool was seriously calcified and his levels were low because every pound he put in was now adding to his calcification. Filter cartridge destroyed and the reason was a combined high Ph with additional Ca introduced because the store tech didn't have anything but a computer programmed with perfect numbers and no practical experience. It took me 2 weeks to save this guys pool and still cost him over $400 dollars with a new cartridge as well.

Bottom line it's a case by case basis with those numbers primarily as guidelines from that point on a well experienced tech has to take all circumstances into account and adjust accordingly which is why it's so difficult to give advice on the internet and up until now I avoided it... It's a much more valuable skill then most people realize.

[fdimike]

Great posting Warp. Thanks for all the helpful info and explanation.

[Naam]

Back when, where you come from the most common pool surface was Marcite until laws removed asbestos as the catalyst which made it substantially softer and shortlived and it was very basic and lime based as is the more recent products like Diamond bright or Pebble tech so a Ph that low would knock years off of the life expectancy of those surfaces which is quite expensive to replace.

please use correct spelling Warp! it is "marshite" not "marcite".

p.s. where i come from there is no marshite, no pebble tec and none of that kind of rubbish. pools in my home country Germany are tiled.

Edited August 18, 2011 by Naam

[WarpSpeed]

Back when, where you come from the most common pool surface was Marcite until laws removed asbestos as the catalyst which made it substantially softer and shortlived and it was very basic and lime based as is the more recent products like Diamond bright or Pebble tech so a Ph that low would knock years off of the life expectancy of those surfaces which is quite expensive to replace.

please use correct spelling Warp! it is "marshite" not "marcite".

p.s. where i come from there is no marshite, no pebble tec and none of that kind of rubbish. pools in my home country Germany are tiled.

Eh? I thought you posted a pool from Florida saying you couldn't get a company to plumb in your system? Ok reading back may be not "where you're from" originally but Florida was my target in that post sorry if that was somehow confusing?

It didn't use to be "marshite" until they had to remove the asbestos fibers but now I understand they have actually allowed using it again but with safety precautions such as masks when applying it as once applied it has no ill effects.. I can't confirm that though as it seems to be a change made since I left, but back in the day a marcite pool would last 10-15 years with proper care and maintenance.

I hate tile in an entire pool it's much harder to care for and that's a personal opinion, too slippery to swim in it's a real hazard, easy to pull a muscle or hurt yourself and dangerous for poor swimmers plus almost impossible to do any free form pools with and make them look half decent so you're limited to box shapes with flat bottoms..

I say harder to care for because tile grout is much softer and in smaller quantities throughout then a surface like marcite or pebble tech so it deteriorates more easily and once a tile pool leaks! Forget about it!! The water channels behind the tiles once the grout is gone and the only solution is a complete draining and re-grouting.. It's like taking care of a spa which is also very difficult, the pool surface does aid in proper water balance and predictability..

Edited August 18, 2011 by WarpSpeed