Stain Removal Process - Calcium Issue

[Buh]

Hello all,

I'm dealing with a staining issue in a fiberglas inground swimming pool. The removal process has been completed, and now I'm left with a blue cloudy pool. Clearing this up will be easy enough. So far everything has gone as planned (I've done this many times over the years) with the exception of 're-balance' day.

The lab results (Taylor lab) show something I've never seen before. Here are the results leading up to my confusion.

AFTER stain treatment:

Salt: 2800ppm

F. Chl: 0ppm

T. Chl: 0ppm

pH: 7.0 (adjusted 6.3)

Alk: 140ppm (adjusted 133)

Stabilizer (CYA): 100ppm (true value)

C.H.: 270ppm

24 hours later the stain removal process was completed - vacuum and backwash etc. 4 hours later the re-balance process began. pH down was added, followed by pH up 4 hours later (40,000L pool). The salt system decided to fail and chlorine tablets were placed in the skimmer. A shock was NOT used. A clarifier was also added.

Today, 24 hours later the test results show:

Salt: 2700ppm

F. Chl: 0.6ppm

T. Chl: 1.8ppm

pH: 7.0 (adjusted 6.2)

Alk: 130ppm (adjusted 127)

Stabilizer (CYA): 60ppm

C.H.: 0ppm

The CYA dropped and the calcium disappeared. Two water analysis were done to confirm this by several people.

After all this rambling, my end question is this: Can anyone shed any possibilities as to how this may have happened? I find this very odd and can think of no scenerio to explain this.

Thank you for any input you have to offer.

Canadian Buh

[waterbear]

First, since you have a fiberglass pool i assume we are talking about iron stains (which are the most common in fiberglass pools and often come from the salt used for SWCG, which is why I like to use solar salt!) Am I correct? Now a few pertinent points to consider:

I have NO IDEA WHATSOEVER what an 'adjusted pH' is. I have never heard of it and it is NOT a part of any Taylor test. Adjusted TA means that the cyanurate alkalinity has been removed from the reading BUT with a CYA reading of 60 to 100 ppm then the 'adjustement" should be in the neighborhood of 10 to 20 ppm and not the 3 to 7 ppm you reported! As to why your test results are what they are I suspect:

1. testing error based on the obviously very low pH and some chemical interferences I will list below.

2. the CYA testing error is because you reported that the pool is cloudy and the CYA test is a turbitity test. If you are starting with cloudy water the test is going to read high, I suspect in the second test the water was clearer. You stated that you added a clarifier. This would explain the APPARENT drop in CYA. My suspicion is that the first reading was a false high because of the turbidity of the water from the stain treatment

Also why did you add pH down and then pH up? This makes NO sense at all. Your pH is TOO LOW and needs to be brought up a bit. THERE IS NO WAY TO KNOW HOW LOW THE pH IS WHEN IT TESTS AT THE BOTTOM OF A PHENOL RED pH TEST UNLESS YOU USE A THREE POINT CALIBRATED pH METER!!!!!!!! There is NO adjustment you can make to the phenol red test that will allow it to read out of range. If you mean the acid and base demand test you have used it incorrectly! IT does not allow you to extend or 'adjust' the range of the phenol red test!

Are you doing the testing yourself or is this a store using a Taylor lab? If it is a store run away from them as fast as possible and get yourself a Taylor K-2006 and do your own testing. If you are testing yourself yo need to learn how to test.

What exactly did you use for stain removal? Remember calcium is a metal and if you added a large dose of sequestrant it can impact your calcium hardness reading.

What kind of salt system do you have and why did it 'decide to fail'? (Exactly what happened?) Certain stain removal products create a huge chlorine demand (which is why you drop the chlorine to close to 0 ppm and add polyquat to help prevent an algae outbreak before using them) and you need to SLOWLY bring the chlorine level back at the risk of redepositing the stain.

Overall I see a lot of testing error by someone who is not really familiar with water testing and the interferences that can give incorrect results I also see some very stange chemical additions that make no sense at all in conjunction with stain removal.

[Buh]

We are talking about copper stains.

Adjusted pH is the number given depending on how many base or acid drops are required - thus the system can calculate how much of what product to add. This calculation is determined by our program - The Prof2 created by Sani-Marc.

I reported 3 to 7ppm of what? The original CYA reading of 100ppm was taken with a clear pool, the 60ppm was taken with a cloudy pool.

The pH down was used to lower the alkalinity. This DOES make sense. The pH up was used to bring the pH up. We are using a dry acid, and we both know this is how alkalinity and pH are adjusted. I'm not sure why this seems to be mind boggling. I will agree timing might have been to close together with the additions.

The phenol test allows for 10 drops base or acid depending which way you're going. It is possible to add the max with no apparent color change. You know this - so am I not understanding what you're trying to say?!

I'm using the TLK204 Wise Lab. I've been using the lab for over 6 years. I'm all for learning more, but I can say I'm quite comfortable with using this lab.

The products used were: http://www.lawrasons.com/POOLSPA/spotlight/index2.html The Stain Out and Stain Prevent.

The salt cell has been confirmed in need of replacement. The cell is 5 years old. I understand the demand on chlorine during the process. This pool has been on our radar for sometime - we are quite familiar with it. The clients have not taken care of the water chemistry ever.

You are NOT dealing with someone new in dealing with this process, nor chemical application. I didn't come here to get flamed or insulted. Nothing mentioned above is considered 'strange' by means of assuming I have no idea what I'm doing.

I know this is beyond 'weird' and near impossible to achieve. I'm not convinced the calcium level is at '0'. This morning a sample was taken again supporting 0ppm calcium. I've never come across anything remotely like this that would lead to a test malfunction to cause the calcium to 'hide' with no signs of a kick out etc.

The removal process was completed Tuesday afternoon. Nothing was done on Wednesday due to time restraints. Thursday a new sample was tested showing 270ppm calcium. Friday, 3 samples were taken tested multiple times showing 0ppm calcium. Saturday morning another sample was tested, still showing 0ppm in calcium. The pool is clear.

[chem geek]

Can anyone shed any possibilities as to how this may have happened? I find this very odd and can think of no scenerio to explain this.

With the chlorine level at 0 ppm during the stain treatment process and with your not using an algaecide such as Polyquat 60 during the process it is possible that bacteria grew and converted some of the CYA into ammonia, nitrite, nitrate or nitrogen gas. Technical details about this are in the thread Degradation of Cyanuric Acid (CYA). If the CYA dropped by 40 ppm and converted to ammonia, it would take up to 3 times that amount of 120 ppm FC cumulatively added to oxidize it. Hopefully that didn't happen -- if it did, then adding chlorine would tend to increase Combined Chlorine (CC), but FC would tend to stay at 0 (assuming you measure after the chlorine mixes with the pool water). You can do a bucket test to see the true chlorine demand by taking a large bucket of pool water and adding chlorine to it until you get an FC reading that holds. 1/4 teaspoon of 6% bleach in 2 gallons is 10 ppm FC.

[waterbear]

We are talking about copper stains.

What color are the stains? Fiberglass is commonly stained black by copper unless it is stained by copper cyanurate, which can happen at a CYA of 100 ppm or higher under the right conditions. Copper cyanurate stains are lavender ("purple haze").

Adjusted pH is the number given depending on how many base or acid drops are required - thus the system can calculate how much of what product to add. This calculation is determined by our program - The Prof2 created by Sani-Marc.

This is a non standard usage of the acid and base demand tests. Once again I repeat, if the sample is out of range of the indicator used you need to use a different indicator or a pH meter. This is standard water testing procedure. I checked out the Sani-Marc websites and found so much just plain wrong information. Here is an example of a direct quote from their website: "Bromine pools can benefit from the use of stabilizer and stabilizer is only required in outdoor pools where UV rays can come in direct contact with the water."

Stabilizer does NOT protect bromine from degredation by UV. Period! IF this is the company you are getting your chemical info from I would start looking elsewhere.

Here is another example of misinformation concerning calcium hardness: "For instance, water that has ‘Low Calcium Hardness’ can corrode equipment or cause etching in some pool surfaces. High ‘Hardness’ can lead to cloudy water or scale."

There is NO evidence that low calcium levels will corrode metal. In fact, chloride and sulfate levels are much more indicative of metal corrosion. Low calcium can etch plaster.

I reported 3 to 7ppm of what?

the difference between the TA and adjusted TA readings. With the pH around 6.0 as you "reported" the adjusted TA should be about 10% to 15% of the total CYA so in the first when the CYA was 100 ppm the adjusted TA should have been 10-15 ppm lower and not only 7 ppm lower as you reported. Anyway, at a pH that low it is not important to adjust the TA for cyanurates since the amount added is just about the precision of the titration test. (1 drop or 10 ppm iwth a 25 ml sample.)

The original CYA reading of 100ppm was taken with a clear pool, the 60ppm was taken with a cloudy pool.

AFTER stain treatment:

Stabilizer (CYA): 100ppm (true value)

C.H.: 270ppm

24 hours later the stain removal process was completed - vacuum and backwash etc. 4 hours later the re-balance process began. pH down was added, followed by pH up 4 hours later (40,000L pool). The salt system decided to fail and chlorine tablets were placed in the skimmer. A shock was NOT used. A clarifier was also added.

Today, 24 hours later the test results show:

Stabilizer (CYA): 60ppm

C.H.: 0ppm

The CYA dropped and the calcium disappeared.

Please reread what you posted. It appears that after the stain treatment the CYA was 100ppm (normal level) and a clarifier was added (which would only be needed if the pool was cloudy). and 24 hours after the completetion (or 48 hours later) the CYA had dropped (and it is assumed the pool had cleared.) Pretty standard procedure for an ascorbic acid treatment (which I will discuss more later). If you do not feel the difference in CYA readings was not testing error or turbidity differences between the samples then chem geek has given you a very viable explanation as to what might have happened to the disappearing CYA.

The pH down was used to lower the alkalinity. This DOES make sense. The pH up was used to bring the pH up. We are using a dry acid, and we both know this is how alkalinity and pH are adjusted. I'm not sure why this seems to be mind boggling. I will agree timing might have been to close together with the additions.

Read and study this. You will learn something you obviously do not know. Please also click on the two links in the second paragraph and read both papers. The first one was printed in the Journal of the Swimming Pool and Spa Industry in 1995 so this is NOT new information by any stretch but the misinformation is so entrenched in our industry that it just does not die! Many pool pros fall into this trap every day!

The phenol test allows for 10 drops base or acid depending which way you're going. It is possible to add the max with no apparent color change. You know this - so am I not understanding what you're trying to say?! I'm using the TLK204 Wise Lab. I've been using the lab for over 6 years. I'm all for learning more, but I can say I'm quite comfortable with using this lab.

The acid and base demand tests are to determine how much acid (muriatic or sodium bisulfate) or soda ash to add to move the pH to a desired point WITHIN THE RANGE OF PHENOL RED INDICATOR, NOT ALLOW YOU TO DETERMINE WHAT THE pH IS WHEN THE INDICATOR IS READING EITHER THE LOWEST OR HIGHEST READING.

I repeat, The acid and base demand tests are to determine how much acid (muriatic or sodium bisulfate) or soda ash to add to move the pH to a desired point WITHIN THE RANGE OF PHENOL RED INDICATOR, NOT ALLOW YOU TO DETERMINE WHAT THE pH IS WHEN THE INDICATOR IS READING EITHER THE LOWEST OR HIGHEST READING.

What you are doing is NOT what the acid and base demand tests are meant to do!

The products used were: http://www.lawrasons...ght/index2.html; The Stain Out and Stain Prevent.

OK now we are at the meat of the "disappearing calcium" and the answer is easy. Just read on and it will all soon be clear!

The products you used are ascorbic acid and EDTA, which I am very familiar with for stain removal. The ascorbic acid is a reducing agent that reduces metals to a colorless and soluble oxidation state. It usually not effective on copper stain on a fiberglass pool but very effective on iron stains and cobalt spotting. This is why I asked earlier what the color of the stains were and the source of the copper. Ascorbic acid will drop pH and TA somewhat but it should not have been as low as you posted unless it was dosed at a very high level, Normally it is 1/2 to 1 lb per 10k gal. (1 to 2 kilos to 40000 liters) Per the instructions on the Larswrason's website you should have adjusted the pH up and the TA down BEFORE you added the ascorbic acid. It does not appear this was done based on your test numbers. This is the first problem.

Now, ascorbic acid is good at removing stains but to keep them away the now dissolved metals need to be 'sequesterd' to keep them from redepositing as stain and also the sanitizer level has to be brought up very slowly, along with the now what should be low TA so the stain does not redeposit. Our choice for sequestering agents are either HEDP or EDTA. HEDP, 1-Hydroxyethylidene 1,1-diphosphonic acid, is the preferred one (yes it does break down to orthophospate but phosphates are really a non issue if the santizer is maintained at proper levels for the CYA, which for a salt pool would be 5% of the CYA level.) EDTA breaks down much more quickly so it is not as effective. Either one needs to be re dosed on a regular basis to keep the stains from reoccuring since neither one really removes them from the water, just deactivates them so they are not as reactive. The one you used is EDTA, ethylenediaminetetracetic acid (as the sodium salt.)

http://www.lawrasons...tainprevent.pdf

Now on to the calcium!

First, realize that calcium IS a metal and as such is affected to one degree or another by a sequestrant added to the water. As it happens HEDP has a higher chelation index for copper and iron than calcium but EDTA chelates calcium and magnesium (which are what make water 'hard') very effectively. In fact, let us review how the calcium hardness test is performed:

1) sodium hydroxide is added to the sample to bring the pH above 10 so magnesium will precipitate out as magnesium hydroxide so we are only titrating calcum (R-0010 http://www.taylortec.../MSDSS/0010.PDF)

2) the calcon indicator is added and turns pink if calcium is present. If there is no calcium it stays blue. http://www.taylortec...MSDSS/0011L.PDF

3) we then titrate with the R-0012 titrant which is EDTA . This reacts with the calcium in the water and 'deactivates' it so it no longer reacts with the calcon indicator which then turns back to blue when there is no more calcium for it to react with because it has all be seqeustered! http://www.taylortec.../MSDSS/0012.PDF

Have you figures out what happened to your calcium yet? Here is a hint, look again at the MSDS for the stain prevent again!

http://www.lawrasons...tainprevent.pdf

Now look at the MSDS for the R-0012 again.

http://www.taylortec.../MSDSS/0012.PDF

The salt cell has been confirmed in need of replacement. The cell is 5 years old. I understand the demand on chlorine during the process. This pool has been on our radar for sometime - we are quite familiar with it. The clients have not taken care of the water chemistry ever. You are NOT dealing with someone new in dealing with this process, nor chemical application. I didn't come here to get flamed or insulted. Nothing mentioned above is considered 'strange' by means of assuming I have no idea what I'm doing.

I am not flaming you, just trying to educate you. There is a lot of misinformation about water chemistry in our industry and we a held captive by what the chemical companies want to tell us. Anything that might hurt their bottom line they tend to misinform us about and that is nothing new.

I know this is beyond 'weird' and near impossible to achieve. I'm not convinced the calcium level is at '0'.

You are right, the calcium is NOT 0 ppm and now you know why it is testing as such!

This morning a sample was taken again supporting 0ppm calcium. I've never come across anything remotely like this that would lead to a test malfunction to cause the calcium to 'hide' with no signs of a kick out etc.

I have encountered it many times myself. It is not uncommon when EDTA is used as a sequestrant.

It does help to have a chemistry background and be familiar with standard testing procedures and not just the instructions that come with a testing lab to be able to understand what is going on. You should have that knowledge now yourself.

The removal process was completed Tuesday afternoon. Nothing was done on Wednesday due to time restraints. Thursday a new sample was tested showing 270ppm calcium. ;Friday, 3 samples were taken tested multiple times showing 0ppm calcium. Saturday morning another sample was tested, still showing 0ppm in calcium. The pool is clear.

Hopefully you knowledge of water chemistry has grown and you will not encounter the same problems in the future! As I said before, I was not flaming or insulting you. You just fell into one of the all to common traps in our industry of having only a bit of knowledge of pool chemicals and testing procedures and, as they say, a little knowledge can be dangerous!

[Buh]

I'll be damned.

I've spent the last hour reading your post, then re-reading, and reading more. When I thought I had it, I read it again. I've had training by many different chemical companies over the years - they all say the same thing. YOU are the first to show proof of what REALLY happens.

I'll read this again tomorrow.

Thank you for your invaluable information and taking the time to educate me.

Chem geek, thank you as well - all the pieces have come together now.

[waterbear]

Welcome to the fourm... I hope you keep posting and contributing!