Severe pH problems, won't stay down.

[matbl]

Hi

I'm seeking some advice on some severe pH problems.
If anyone is able to come up with a solution for what is basically a chemistry problem, I would be very grateful.

Basics:
I have a too high pH in my pool of 8.0.
I can adjust it with normal pH lowering product which I expect is sodium bisulphate.
It goes down as expected.
But then it goes back up to 8.0 (see picture, time scale is 1 week)
ORP goes up as expected when pH goes down.

I do have a salt chlorinator but it was turned off during the measurement period.
No other chemicals have been added during this period.
Other than pH being high, the pool water is clean and nice.

I can repeat the same adjustment with the same end results every time.

More information:
pH probe is calibrated.
Water measurement has been done by an accredited laboratory which confirms pH reading.
Laboratory also reports the following chemical levels:
(all in ppm unless otherwise specified)
Alkalinity, HCO3: 57
NH4-N: 0
NH4: 0
NO3-N: 2.7
NO2-N: 0
NO2: 0
PO4-P: 0.072
PO4: 0.22
F: 0.13
SO4: 330
Fe: 0
Ca: 51
K: 7.0
Cu: 0
Mg: 5.0
Mn: 0
Na: 1500
CaCO3: 150 (translated from hardness)

Free chlorine as measured by simple aquacheck sticks is 0 - 0.5.
CYA is 0.

I can't really wrap my head around this.
What on earth is causing pH to go back up?

 

[cowboycasey]

Welcome to TFP

The problem you say you have is not a problem at all... Please start using muriatic acid to drop you PH and TA as it will not hurt the SWG like the sodium Bisulfate will...

With a TA of 150 your PH will rise faster than if you had TA at the recommended levels ( TA about 80 ) A week is actually a very good PH rise for a TA of 150..

Now lets get down to what you actually have wrong..

SWG hate to raise FC, they do really great at keeping FC at a constant level... But with no CYA the sun is burning off the FC before it can keep your pool safe.. Guess strips are not worth the paper they are on, they are really bad, maybe the first 1 or 2 strips "may" be close but by the 3rd check they are so off we never trust them...

What We would recommend Recommended Levels

1. Continue dropping PH when it reaches 7.8 using muriatic acid down to 7.0, by doing this your TA will also go down...
2 Bring your CYA to 70 and FC to 7, your SWG will love life and your pool will sail through life being happy as a clam

the next one is hard for you.. Test kits... The best test kits are Taylor drop based kit but they are very hard to get over there... The Taylor K-2006C is the best and some have gotten them there...

I hope this helps

 

[matbl]

Hi

Thank you.

The sodium bisulphate hurts the SWG? Doesn't sound good. In what way? Does it corrode the plates?

Muriatic acid is HCl right? Near impossible to get here but will try to start using it instead.

Alkalinity is 57, not 150, measured by accredited laboratory.
If it had been 150, I had agreed with your conclusion. But with ~60, I don't get why the pH is rising again.
The full graph is about a week, the pH rises from 7.0 to ~7.7 in a day.

FC at 7 ppm? That's insanely high. Why? Or do you mean 0.7?
I get perfectly fine ORP levels with FC at ~0.5 and this is regulated very well by the SWG.
As it's much better to measure ORP than FC since it will give a direct measurement of disinfection capability I see no reason to have a higher FC.
But then again, at CYA 70 you do need insanely high FC levels to get decent ORP.
I prefer to keep CYA at 0 since I then also can keep the FC very low. After all, the point of chlorine is as disinfection in the water.

To reiterate, my water is perfectly clean at very low chlorine levels. It was measured by the same laboratory to be suitable as tap water.
Only question is why I can't get the pH down.
I know the SWG raises pH but it was turned off here.

Maybe I should mention that I have a sliding roof over the pool so I don't get any rain water or debris in it at all.

 

[ajw22]

The sodium bisulphate hurts the SWG? Doesn't sound good. In what way? Does it corrode the plates?

From Acid - Further Reading

Dry acid can be used to lower pH and TA. However dry acid contains sulfates which will accumulate in the water. Dry acid should not be used in plaster pools or pools with a SWG.

Dry acid is often sold as “pH Minus.”

Dry acid is sodium bisulfate. After dissociation of the acid salt, it leaves behind the sulfate ion.

Problems sulfates can cause include:

• Sulfates can damage concrete & plaster
• Excess sulfates in water increases the likelihood of corrosion on metal parts
• Excess sulfates in splash out water leads to degradation of any concrete surfaces
• Sulfates degrade the coatings on SWG plates
• At high enough concentrations, sulfates can react with calcium to form spindly, needle-like crystals of calcium sulfate (gypsum)
• While sulfates in vinyl pools is typically not as problematic as in plaster pools, scaling of gypsum crystals can increase the risk of liner puncture.[9]

Sulfates can only be removed by draining water.

Pentair specifically says on page 9 in the IntelliChlor SWG Manual[10] - CAUTION: The use of dry acid (sodium bisulfate) to adjust pool pH is discouraged especially in arid regions where pool water is subject to excessive evaporation and is not commonly diluted with fresh water. Dry acid can cause a buildup of by-products that can damage your chlorinator cell.

Only question is why I can't get the pH down.

A pH of 8 is not severe or a major problem. Low pH can cause damage. High pH may cause scale but does not damage equipment.

Let's be clear, you can get your pH down using acid. The pH just does not stay stable for any length of time. That is likely caused by your TA.

We have a different view of the proper pool water chemistry then you do. I suggest you get familiar with TFP methods as it is being effectively used in thousands of pools.

ABC's of Pool Water Chemistry

There are several items things every pool owner should know about swimming pool water. We share details on the basics of Pool Water Chemistry.

www.troublefreepool.com

Pool Care Basics Archives

Your one-stop shop for all things TFP to include: ABCs of Water Chemistry, Recommended Chemicals/Levels, Test Kits, Troubleshooting, and much more!

www.troublefreepool.com

PH - Further Reading

www.troublefreepool.com

TA - Further Reading

www.troublefreepool.com

 

[cowboycasey]

If you are depending on ORP then a high CYA or just about any CYA will mess with it...

SWG does not keep PH raised. The PH does rise a little while the water is inside the cell but it comes back down after it comes out the cell... it does not stay high... Most of the time people think a SWG makes PH rise is because the come form using pucks and then change to a SWG... The pucks are acidic and keep the PH down, that is why they recommend a TA of 150 or so when using pucks...

TFP-TV

A collection of Videos from the source you trust the most, TFP! These videos are to help the average homeowner understand their pool and enjoy their water.

www.troublefreepool.com

Check out the TA PH video here

 

[Flying Tivo]

Do you have any water features? Like, fountains, waterfalls, laminars? Do you have a Spa attached to the pool? Aeration can cause rapid rise in PH. Please fill in your signature with your pool and equipment specs, so we can help you better. As an example look at mine down below.

 

[JoyfulNoise]

Is the carbonate alkalinity in that water report measured as "ppm of [HCO3]" (parts per million of bicarbonate ion) OR is it measured in the more traditional units of "ppm of [CaCO3]" (parts per million of calcium carbonate). Most standard pool test kits that use strong acid titration are standardized against and report values of alkalinity in ppm [CaCO3].

 

[JoyfulNoise]

In order to do some calculations we need to know more info about your pool, specifically its volume and surface type (plaster, vinyl, fiberglass ?).

Generally speaking, your pool is an open system of water in contact with the Earth's atmosphere. So there is always a transfer of CO2 between the highly carbonated pool water (yes, pool water is over-carbonated relative to atmospheric levels of CO2) and the atmosphere. This outgassing of CO2 will cause pH to increase all the time; there is no such thing as stable pH when water has carbonate alkalinity in it and it is in contact with air.

As for your specific pool setup, you have chosen to run the pool using ORP control, an SWG, a pool cover, no CYA and low FC. While that is one way to run a pool, it is not how the vast majority of pools are operated (at least not residential pools in the US). With your setup, you will need to be exceptionally careful at maintaining an FC level of 0.25 to 0.5ppm (which, at zero CYA causes the HOCl levels to be very high and, possibly, irritating to some people) and ensuring that your hydraulic mixing efficiency of your skimmer and returns is adequate. Maintaining such a low FC level consistently and homogeneously throughout the water volume can be difficult. Also, do not confuse oxidation with sanitation (or disinfection). ORP is a measure of the oxidizing potential of water, that has nothing to do with disinfection. One can easily mix up a solution of an oxidizer that gives the same, or higher, ORP value as a mixture of chlorine and yet not be sanitizing at all. Chlorine is both a strong oxidizer and, in the case of most pathogens, a fast sanitizer. However, it is not the case that something that is a strong oxidizer is necessarily a fast sanitizer. An example of that is non-chlorine shock (potassium monopersulfate, or MPS). While MPS is a very strong oxidizer, it is an inadequate sanitizer as it is considered too slow on its own at neutralizing pathogens. Your ORP readings can be considered as "correlated to FC" but FC should be checked regularly to ensure that you are not getting false ORP readings. Many ORP probes are consumable items that need to be replaced on a regular basis (12-24 months) and the probe should be calibrated regularly using an ORP standard to ensure accuracy. Likewise, pH probes are not "forever" and need to be replaced regularly as well. They too should be calibrated often against a standard to ensure that they are in good working order.