pH and alkalinity are low and nothing seems to raise them

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TristanPT

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Jul 13, 2024
9
Lisbon, Portugal
We have an in-ground pool of around 5000 gallons and since we have owned the property, the water has been stubbornly acidic. A phenol red test is always yellow so I tried some litmus paper and it claims a pH of about 3. We do use the pool and it is not too bad but skin feels a little sore sometimes.

I got some test strips and they also report that the alkalinity is basically 0. I know that reading the strips is quite subjective but I put a test strip in some diluted bicarb and it showed a vivid colour for alkalinity, so they do work but there is no colour change at all in the pool water.

We use all-in-one tablets for the pool chemicals and I have read that they have a pH of 3 which explains why the water is so acidic.

The tablets we currently use are these (sorry, it's in Portuguese): https://www.leroymerlin.pt/produtos...efeitos-para-piscina-4-kg-axton-86761794.html

We don't know what we are supposed to do to get the pH up to the normal range, and the alkalinity up to help keep it there. I have tried to add soda ash last summer and bicarb this summer and neither of them make any change to the pH or alkalinity. We are afraid to just keep throwing in different chemicals to try to resolve this and make the water more pleasant.

I have read that pH should naturally raise anyway, but that doesn't seem to happen. I have angled the filter return jets up to disturb the surface a bit and maybe release CO from the water but it didn't help. The pool has a hard cover that we only open when we use it, so maybe the CO dissolves into the water again.

What else can we try?
 
Welcome to TFP.

What do your pH and alkalinity tests tell you about your tap water?
 
1 kg of bicarbonate will add 30 ppm TA to 5000 gallons. Add that amount, circulate for thirty minutes, test TA, repeat until you get a TA above 70 ppm.

The tablets you are using are acidic. You need to add bicarbonate every time you add new tablets.
 
Thank you for the replies.

> What do your pH and alkalinity tests tell you about your tap water?
Our tap water is 40 ppm for alkalinity (using a test strip) and about pH 6.5 (using litmus paper).

> 1 kg of bicarbonate will add 30 ppm TA to 5000 gallons.
I already tried 2kg of bicarbonate (in two rounds of 1kg a week apart) and there was no measurable change to the alkalinity. Should I keep going?
Will this also raise the pH sufficiently?

> You need to add bicarbonate every time you add new tablets.
How do I calculate the amount I need to add to balance the tablets, or is it trial and error once I get the alkalinity up?
 
50 lbs of trichlor in a 25,000 gallon pool will:

Raise fc by 219 ppm

Raise CYA by 133 ppm

Raise salt by 179 ppm

Lower TA by 154 ppm

To raise TA by 154 ppm, you need 63 lb of baking soda.

So, you need 1.14 lb baking soda per lb of trichlor to offset the TA loss.

7 lb of trichlor requires 8 lb of baking soda to keep the TA constant.

In the above case with a CYA of 133 ppm, the CYA contributes about 133/3 = 44 ppm of the TA.

So, if the Carbonate Alkalinity started at 100 ppm the TA would also be 100 ppm.

However, at CYA = 133 ppm, the carbonate alkalinity will be 100 - 44 = 56 ppm.

To keep the carbonate alkalinity constant, you would need to end up with a TA of 144.

So, you need to add 154 + 44 = 198 ppm.

To raise TA by 198 ppm in 25,000 gallons, you need 73 lb of baking soda.

You need 1.46 lb baking soda per lb of trichlor to keep the carbonate alkalinity constant.

10 lbs of trichlor requires 11.4 lbs of baking soda to keep the Total Alkalinity constant.

10 lbs of trichlor requires 14.6 lbs of baking soda to keep the Carbonate Alkalinity constant.
 
What is the CYA level?

You need a good drop test kit like the Taylor K-2006C.

When the TA is immediately red, the TA is 0 or negative.

To calculate the actual TA, I use R-0006 base demand to titrate from red to green and then multiply the result by 6.3 to see how negative the TA is.
 
50 lbs of trichlor in a 25,000 gallon pool will:

Raise fc by 219 ppm

Raise CYA by 133 ppm

Raise salt by 179 ppm

Lower TA by 154 ppm.

For example, if the TA started at 40 ppm and you used 50 lbs of trichlor in a 25,000 gallon pool, the TA would be 40 - 154 = -114 ppm.

Your CYA level can tell you how much tablets have been used.

For example, if the CYA was 100, the tablet use can be calculated as 50 x 100/133 = 37.6 lbs used.

The TA can be calculated as 40 - (154 x 100/133) = -76 ppm.
 
K-2006 is correct.

Can you get a different drop based test kit with TA, pH and base demand?

Can you drain and refill the pool so that you are starting with better water?

Note that draining can cause damage to the pool and it should not be done unless you can verify that it is safe to do so.
 
I haven't found another drop based test kit. I can try to get a K-2006 in the UK and put it in the hold on the plane but I worry it wouldn't get through in hand baggage.

We did drain and refill the pool last year because we had failed to get the water under control since buying the property and it survived the process, but we just ended up in the same situation by using the tablets.

It cost about €250 in water to refill so if there is a cheaper way to balance the water, it is preferable.

Should we be trying to get the alkalinity correct first, and then the pH? If so, I can keep adding more bicarb to see it anything happens.

I am only vaguely familiar with pool chemistry so all of these acronyms only mean a little to me. On paper, adding bicarb should do something but I am not seeing any change at all and I don't understand why.

If I can balance the water and can get a drop based test kit, is it better to switch to using specific chemicals instead of the tablets to keep the water balanced?
 

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TristanPT said:
Should we be trying to get the alkalinity correct first, and then the pH? If so, I can keep adding more bicarb to see it anything happens.
Click to expand...
mknauss said:
1 kg of bicarbonate will add 30 ppm TA to 5000 gallons. Add that amount, circulate for thirty minutes, test TA, repeat until you get a TA above 70 ppm.
Click to expand...
 
TristanPT said:
On paper, adding bicarb should do something but I am not seeing any change at all and I don't understand why.
Click to expand...
The Total Alkalinity can be negative.

For example, if the alkalinity is -150, you would have to increase the TA by more than 150 ppm just to get a reading.

Can you measure the cyanuric acid level?

Most likely, the CYA (Cyanuric Acid) level is way over 100 ppm and this requires a significant dilution.
 
When the TA is immediately red, the TA is 0 or negative.

To calculate the actual TA, I use R-0006 base demand to titrate from red to green and then multiply the result by 6.3 to see how negative the TA is.

Edit - The multiplier might be 3.6 and not 6.3.

I will try to find the original calculation.

In any case, the difference is not that much and you are only trying to get a rough idea about how negative the TA is.

You can also use R-0010 Calcium Buffer to titrate and the multiplier is 33 ppm per drop.

1721090419533.png

1721090540021.png

1721090572931.png
 
Last edited:
> The Total Alkalinity can be negative.
Ok, that is new information. I didn't know this. I was getting frustrated that I was throwing stuff in the water and nothing was happening.

> Can you measure the cyanuric acid level?
My test strips claim to measure CYA but that doesn't change colour at all. The range is orange to light purple but it stays the same pale yellow as it is when it is dry.

> You can use sodium hypochlorite instead of trichlor tablets.
We tried this when we first bought the property but the water was already unbalanced so we never figured out how to balance it. A neighbour suggested tablets because that is all they use.

> Can you get a salt system?
This has been suggested to us. It apparently costs about €2,000 to do but it is something we would consider.

> Can you measure the salinity?
No. I wouldn't know how.

I guess I'll keep going with gradually adding bicarb for now, and try to get a drop test kit to get better information.
 
> try to get a drop test kit to get better information.

I found I can get one shipped to Portugal from the UK.

One question, what's the lifespan of a Taylor K-2006 kit? Do they last for several years, either based on the amount of the chemicals and a sensible testing interval, or just lifespan of the chemicals themselves?
If I have to spend £125 a year on a test kit, plus the cost of chemicals to balance the water, it starts to look cheaper to just drain and refill the pool once a year and keep using the tablets.
 
TristanPT said:
One question, what's the lifespan of a Taylor K-2006 kit? Do they last for several years, either based on the amount of the chemicals and a sensible testing interval, or just lifespan of the chemicals themselves?
Click to expand...

Taylor recommends replacing reagents annually. If stored in a cool dry place out of the sun you can stretch fresh reagents to 2 years.

TristanPT said:
If I have to spend £125 a year on a test kit, plus the cost of chemicals to balance the water, it starts to look cheaper to just drain and refill the pool once a year and keep using the tablets.
Click to expand...
With 5000 gallons draining and refilling to get a known good water chemistry may be your best plan.
 
JamesW said:
When the TA is immediately red, the TA is 0 or negative.

To calculate the actual TA, I use R-0006 base demand to titrate from red to green and then multiply the result by 6.3 to see how negative the TA is.

Edit - The multiplier might be 3.6 and not 6.3.

I will try to find the original calculation.

In any case, the difference is not that much and you are only trying to get a rough idea about how negative the TA is.

You can also use R-0010 Calcium Buffer to titrate and the multiplier is 33 ppm per drop.

View attachment 596464

View attachment 596465

View attachment 596466
Click to expand...
Could you write how you calculate TA using R-0006 step by step?

Thanks
 

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