Calcium Problem (?) and Constant High PH

[Davo123]

Looking for some advice on correcting the issues of Calcium build up and the inability to lower the PH. We have moved into a house approximately 18 months ago and have been battling with issues of a calcium problem (assumed) and a constant high PH level.
In summary:
Pool is in Queensland, Australia

1. 45,000 litre saltwater pebblecrete pool
2. Yellowing of the surface in patches and around the waterline, which I assume is calcium buildup
3. Constant high PH (8.2 - 8.4) despite adding at least 5 litres of acid (over a 4-5 month period)
4. Acid demand 2 drops (equates to need to add approx 400 ml acid??)
5. Salt water chlorinator cell has been cleaned but CL level remains around 1.2 - 1.5
6. Salt concentration is around 6000 ppm which is the specified level for the brand of chlorinator

My assumption is that the pool was not properly looked after for a long period, hence the calcium issue.
Also, my thoughts are that the high calcium level may be neutralizing the acid, which is probably why I am having trouble dropping the PH level.
I did read somewhere that a possible cure with the calcium build up would be to drop the PH level to 6.8 for a period to get rid of the calcium issue, and as we are going into winter, this is a possibility.
So, I am looking for the advice from the experts on this forum - suggestions/advice please?

 

[Bperry]

Looking for some advice on correcting the issues of Calcium build up and the inability to lower the PH. We have moved into a house approximately 18 months ago and have been battling with issues of a calcium problem (assumed) and a constant high PH level.
In summary:
Pool is in Queensland, Australia

1. 45,000 litre saltwater pebblecrete pool
2. Yellowing of the surface in patches and around the waterline, which I assume is calcium buildup
3. Constant high PH (8.2 - 8.4) despite adding at least 5 litres of acid (over a 4-5 month period)
4. Acid demand 2 drops (equates to need to add approx 400 ml acid??)
5. Salt water chlorinator cell has been cleaned but CL level remains around 1.2 - 1.5
6. Salt concentration is around 6000 ppm which is the specified level for the brand of chlorinator

My assumption is that the pool was not properly looked after for a long period, hence the calcium issue.
Also, my thoughts are that the high calcium level may be neutralizing the acid, which is probably why I am having trouble dropping the PH level.
I did read somewhere that a possible cure with the calcium build up would be to drop the PH level to 6.8 for a period to get rid of the calcium issue, and as we are going into winter, this is a possibility.
So, I am looking for the advice from the experts on this forum - suggestions/advice please?

Welcome! What is the calcium level? The only way to remove calcium from the water is to drain it and reolace it with fresh water.

Yellowing (or other colors like that) is more comminly algae which would point to low chlorine. If the chlorine is low for any length of time, algae is common. Do you have a reliable test kit?

 

[Davo123]

Hi Bperry, yes, I do have a test kit (purchased within the last 12 months), but it only tests for 4 things, chlorine, PH, Total alkalinity and Acid demand.
Latest figures were:

1. Chlorine 1.5
2. Ph 8.3
3. Acid demand 2 drops (need to add 500 ml acid, AGAIN!)
4. Total alkalinity Not tested the last time.

The chlorine level is on the low side, and the latest reading, taken 6 days ago was 1.5. The chlorinator is gassing quite profusely, so I believe it is producing enough chlorine.
I don't profess to be an expert, but I believe that the yellowing not an algae, as it can't be brushed off with a brush and when running my fingers over it, it feels rough, so I believe it is a deposit of some type and my assumption, based on reading articles, is that it is likely calcium.
Appreciate any thoughts.

 

[Lake Placid]

We’ve got some members in your neck of the woods that can help with test kit advice. @mgtfp @AUSpool @needsajet
We really need to know your calcium hardness levels to give a proper assessment on calcium. Also will need to know your CYA level to understand how low your FC level is with respect to your stabilizer. Can you post pics of the offending stained areas?

 

[needsajet]

Welcome to TFP. Good to have you join us here

Probably a longer conversation than you had in mind, but for starters, you're going to need a drop-based test kit. The one we recommend is Clear Choice Labs, which you'll find online. They're out of stock for the salt water option, so buy the freshwater kit. When their stock improves, you can add a dedicated salt test kit.

In the meantime, what's your alkalinity?

Calcium scale tends to show up near the surface, or just above the surface. Where is the discolouration?

Also, add a signature. Click your username (top right) and then 'signature' (pool size, pool surface, etc.)

 

[AUSpool]

Hi Bperry, yes, I do have a test kit (purchased within the last 12 months), but it only tests for 4 things, chlorine, PH, Total alkalinity and Acid demand.
Latest figures were:

1. Chlorine 1.5
2. Ph 8.3
3. Acid demand 2 drops (need to add 500 ml acid, AGAIN!)
4. Total alkalinity Not tested the last time.

The chlorine level is on the low side, and the latest reading, taken 6 days ago was 1.5. The chlorinator is gassing quite profusely, so I believe it is producing enough chlorine.
I don't profess to be an expert, but I believe that the yellowing not an algae, as it can't be brushed off with a brush and when running my fingers over it, it feels rough, so I believe it is a deposit of some type and my assumption, based on reading articles, is that it is likely calcium.
Appreciate any thoughts.

Geday Davo, welcome to TFP.

A 4in1 is a good start, Aussie gold? But you’re missing a FAS/DPD for free chlorine, FC, calcium hardness, CH, and stabilizer, CYA. You could add these as separate items from Clear Choice Labs but it’s probably better value as a complete kit. Either way you’ll want to keep that pH comparator from the 4in1.

I normally think of calcium stains as white deposits, so I’m guessing there is more to it. Yellow could be mustard algae, pollens and it does tend to implicate iron.

What salt have you been using?
What chlorination do you have? And does it have ORP control?

pH does tend to go up over time and it will go up faster if your TA is high and/or you have water features.

It’s best to set your SWG output according to your desired FC level as indicated by testing. Just thinking the SWG is producing is not enough. Kind of like a car moving but how fast is it moving? And to set your desired FC you’ll need a FAS/DPD FC kit and you’ll need to know your current CyA or stabilizer level. At TFP we treat FC and CyA as co-defendant because they do react and interact with each other. See FC/CYA Levels

Have a read through Pool Care Basics

 

[Davo123]

Apologies for the delayed response. Firstly, I have attached some photos of the stains. The floor one is around the hydrostatic valve, which is obviously at the lowest point, and could possibly be the previous owner tossing in some chemicals and not agitating (just a guess on my part). There are also stains around each of the outlets into the pool as shown in the other two photos. As mentioned previously, there is also some slighter staining around the water line and a swimout ledge where the pool cleaner doesn't reach. In all these places, I have tried to brush the staining off with a stiff brush, but nothing moves.

I did a new water test on the weekend and the figures are as follows:

1. Chlorine 1.8 (I have some doubts on the accuracy of this test as a number of DPD tablets had broken down into a brown mess, but I used one that appeared OK)
2. PH 8.3
3. Acid Demand 2 drops correction
4. Total Alkalinity 1-2 drops which equates to needing to add 500 ml acid (this is the same as previous readings, where in total I have added over 5 litres of acid)

To answer Auspools questions:
What salt have you been using?
Just the normal salt from Bunnings (Sunray), but I have no idea what the previous owners used for the 10 years before that, when I think the issues began.

What chlorination do you have?
The chlorinator is an Austral brand, and I have it set on the maximum output (8)

And does it have ORP control?
No

pH does tend to go up over time and it will go up faster if your TA is high and/or you have water features
There are no water features.

4in1 is a good start, Aussie gold?
Yes. it is an Aussie Gold kit purchased late last year.

I note the need for additional tests, so will look into it.

regards,
Dave

 

[needsajet]

If it's the brown discolouration, there's a pretty good chance that's iron. You can use vitamin C to find out. Best is some uncoloured plain ordinary vitamin C tablets (around 10 tablets) crushed up in the end of a sock (or vitamin C powder bought from a health food store). Hold that up against the brown area in one spot for around a minute or two. See if the colour changed under where you held the sock.

If you have any trichlor tablets, you can use those to test to see if it's established organic matter. Chlorine will bleach organic matter very noticeably, whereas Vitamin C will not. Likewise, chlorine won't affect iron stains.

 

[mgtfp]

Het Davo, welcome!

Also, my thoughts are that the high calcium level may be neutralizing the acid, which is probably why I am having trouble dropping the PH level.

Calcium doesn't neutralise acid. Constantly rising pH is usually caused by TA being too high. It's something to get your head around, because at first we associate better pH buffering with higher TA, and think that higher TA should result in more stable pH. What's missing in the equation is that the main contributor to Total Alkalinjty is Carbonate Alkalinity, i.e. dissolved carbonates. Carbonated water is oversaturated with dissolved carbon dioxide that is constantly outgassing. As it out-gasses, pH rises. Just like an opened bottle of bubbly water.

The TA levels that pool stores recommend are only necessary when using acidic forms of chlorine, like trichlor tabs. These are constantly pulling pH and TA down. The pH rise due to CO2 outgassing is then a welcome effect and compensates the ph-pull from trichlor.

With an SWG (or when using liquid chlorine), there is no pH-pull from the source of chlorine, which makes the pH-rise effect very noticeable. Lower TA levels around 60-70 are more beneficial in this case. Lower TA will also make higher CH more manageable, as it is the product of the calcium and carbonate (which TA is a measure for) concentrations that quantifies the risk for scaling. This is what;s behind the CSI that you can calculate with PoolMath.

Total Alkalinity 1-2 drops which equates to needing to add 500 ml acid (this is the same as previous readings, where in total I have added over 5 litres of acid)

This doesn't really make sense to me. TA of 10-20 is not really compatible with pH above 8. Are you sure that you are doing the TA test correctly? Even though the Aussie Gold uses the same drops for acid demand and TA tests, they are different tests. You are not getting them mixed up? Could describe how you are doing the TA test?

I'd really recommend to get a test kit from Clear Choice Labs. With this, you can test all relevant parameters, including CH, which will allow us to assess the scaling situation better. It also includes the FAS/DPD titration test for Free Chlorine, which is required to follow the TFP method.

 

[Davo123]

Needsajet, you were spot on with your diagnosis! I bought some ascorbic acid, put it in a piece of cloth and held it against the brown stains around the pump outlets and the stains immediately disappeared, so looks like I need to treat the pool with it. Any idea of the dosage; I saw one reference that said 1 kg for 45K litres, and a second that said 0.5 kg, so what do you think I should dose to? Also where is a cheap source of supply?

MGTFP, thanks for your response and explanation on the effect of calcium, which I now believe is not the issue, and it is apparently iron staining, so I need to treat that.
Happy to be corrected, but it appears that the TA is not terribly out, as the test indicated that the ratio is 10-20 Mg/l, and I need to add 400 - 500 ml of acid to correct this.
You are not getting them mixed up? Could describe how you are doing the TA test?
I don't believe that I am doing the test wrong, as I followed the steps, but I could be wrong.......
I can read out the steps I followed from the test kit, but that doesn't prove anything, but I have plotted the results over the last 8 months, and the readings are quite consistent, so my assumption is my methods are correct.


So, I am left with the issue of being unable to pull the PH level down, despite a large quantity (> 5 litres) being added, so should I go down the path of a lot more acid being added, or is there another cause that I should look at, as the other test results are not too far out?

Dave

 

[needsajet]

Yeh hey, there's an article here about the iron treatment. I think I used 800g for mine. It is magical!

However, there's an aftermath worth thinking through carefully. I personally think dumping the water is the cheapest thing to do because of the cost of sequestrant. Changing water has other aspects and significant risks to consider.

I'll find the articles if I can, Pool School

 

[needsajet]

Ascorbic Acid Treatment - Further Reading

www.troublefreepool.com

Draining - Further Reading

www.troublefreepool.com

Have a thorough squizz through those and come up with a plan. Happy to discuss further.

By the way, welcome to TFP! Good to have you here

 

[mgtfp]

You are not getting them mixed up? Could describe how you are doing the TA test?
I don't believe that I am doing the test wrong, as I followed the steps, but I could be wrong.......
I can read out the steps I followed from the test kit, but that doesn't prove anything, but I have plotted the results over the last 8 months, and the readings are quite consistent, so my assumption is my methods are correct.

Just to confirm:

You fill the larger of the two tubes to the Total Alkalinity fill line with pool water, somewhere around the bottom third of the tube.

You add 1 drop of solution 4 which dechlorinates the sample.

You add 2 drops of solution 5, which is the indicator and turns the sample blue.

Then you add drops of solution 3 until the sample turns clearish/greenish or yellow.


And you are saying you need 1 to 2 drops of solution 3 in the last step? That's what baffles me, this means TA of 10-20, which is dangerously low, and the polar opposite to having pH above 8.

 

[Davo123]

Hi MGTFP
I followed your and the test kit method precisely, which are obviously the same steps.
When I added two drops of Solution 5, the water only turned a very slight tinge of blue. It then took 1-2 drops of Solution 3 to turn the water clear. Reading the instructions it said "Count drops needed to change colour from Blue to clear or slightly Yellow", so I thought maybe I should add further drops in see if the water sample turned slightly yellow. I gave up at 25 drops without the sample changing from clear! So my thoughts are that either the Total Alkalinity is really high ((> 25 drops) or there is a problem with the test kit. Either way, I think my priority is to get the PH down by acid dosing, and separately treating the iron residue.
I got new DPD tablets today as the previous batch was suspect, but no real change from previous readings.


Hi needsajet,
I briefly read the information that you enclosed, but I will need to read again carefully to digest all the information. The way forward is ascorbic acid treatment and follow up steps afterwards, and as it is Winter now and no swimming, I can consider the next steps carefully, but changing a percentage of the water may be the first step after AA treatment.

Dave

 

[mgtfp]

OK, let's get a step back first. The TA test works by adding an acid (hydrochloric acid in case of the Aussie Gold test, sulfuric acid in case of the Taylor / Clear Choice Labs test) until you reach pH 4.5 (that's where TA is zero in a buffered water solution).

To know where pH is 4.5, we need a pH indicator:



Taylor / Clear Choice Labs uses a mixture of two indicators (Bromocresol Green and Methyl Red) which changes around pH 5 from green to red, at pH 4.5 the transition is pretty much complete, we therefore add drops until the red doesn't change anymore (and don't count the drop that doesn't cause further colour change).

Aussie Gold (which is just an imported and rebranded Blue Devil Test Kit) uses Bromophenol Blue, which changes from blue to yellow around pH 4, which is actually already a bit too low. Once the colour transition is completed (at yellow), pH is nearly down to 3. You want to catch that point where the colour transition just started. Which is quite hard. And because of the lower transition point you tend to overestimate TA.

That's how it looks like in real life:



For this demonstration I have used the Blue Devil titrating drops in both cases, but I used the Taylor Indicator (identical to Clear Choice Labs) in one case.

The images highlighted in black are what you would pick as titration endpoints in the respective tests - in case of Clear Choice Labs we don't count the last drop that didn't change the shade of red anymore, in case of Aussie Gold we don't count the drop when it went yellow (but sometimes it jumps straight from blue to yellow, then that's your endpoint, of course).

The Clear Choice Labs indicator is much better. I often use the Aussie Gold titrating drops (solution 3), because they are much cheaper, but I always use the Clear Choice Labs indicator (at the moment original Taylor, actually).

Does it look anything like that in your case?

You can try using 4 drops of indicator, that makes the colours a bit clearer.

Maybe your chlorine is higher than you think. Try using one more drop of Thiosulfate (solution 4) in step one to make sure that the sample is fully dechlorinated.

TA 10-20 just doesn't seem right in combination with high pH.

I really suggest to order the Clear Choice Labs test so we can have confidence in your test results.