Wacky Pool readings

Chlorinating, maintaining the right chlorine levels,
chlorine problems. Dichlor, trichlor, cal hypo, bleach,
granules, chlorine pucks and chlorine sticks.

Wacky Pool readings

Postby stantheman » Tue 09 Sep, 2014 16:33


Please could someone help.

I live in london, uk and have had crystal clear waters in my pool (approx 71000l) all summer. However after a recent pool party and my adding of chlorine and ph adjusters, the chemical readings are very strange. I was having difficulty understanding the readings using normal dye tests so went out and bought a SCUBA II digital reader to provide more accurate readings.

The readings I currently have are
Free Chlorine - My meter just says HIGH i.e. above measurable range
Total Chlorine - My meter just says HIGH i.e. above measurable range
Cyuranic Acid = 114
Total Alkalinity = 268

The pool has a turquoise / green tinge to it, there is some residue on the sides of the pool. Having said that it was just about useable today... even though it was no where near its crystal clear blue normal self.

The pool has a vinyl liner and an air source heat pump, with water heated to 30 degrees celcius.

Do I need to wait for chlorine levels to drop over a period of time?
Should I partially drain the pool?
Should I isolate / turn off the heat pump to avoid any damage due to high alkalinity?

Really hope somebody can help with meaningful advice. I would prefer not to drain the pool as it is so large to refill, but will do so if there is no alternative.

Hope you can help!!


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Wacky Pool readings

Postby stantheman » Tue 09 Sep, 2014 16:46

Slight correction. My pool volume is 79,000l.
Also I have been using Stabilised Chlorine Granules.
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Wacky Pool readings

Postby stantheman » Tue 09 Sep, 2014 16:55

One more update... I live in a Hard Water area.. not sure what my calcium levels are.. But london generally has hard water.
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Wacky Pool readings

Postby chem geek » Wed 10 Sep, 2014 02:08

Do you know the limit for your chlorine test? It might be 5 ppm. If your TA and CYA readings are correct, then they are both high. The high CYA will lower the active chlorine level making it more likely to get algae growth. If your CH is also high as you suspect, then yes you have some risk of scaling, especially in the heater and especially if your pH gets higher. You can read the Pool School to learn more about managing your pool. You might consider using chlorinating liquid (Crown or other brand) as your primary source of chlorine to help keep the CYA level in check. The following are chemical facts independent of concentration of product or of pool size:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.
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Wacky Pool readings

Postby stantheman » Wed 10 Sep, 2014 13:26

Thanks Chem Geek for your help.

Appreciate the advice. The pool meter that I have is meant to be quite accurate...

The Chlorine level on my meter reaches up to 6mg /l so we know that chlorine level is higher than this.
I have read that my Cyunaric acid levels should be no more than 100 ppm, so although mine are high... they may not be exceptionally high.

A local pool person has suggested the following

- Keep the pool cover off to help the sunlight breakdown the high chlorine
- Brush the Algae so that it combines with the free chlorine in the water
- Add some fresh water where possible to help dilute
- Drain a little of the old water where possible to help dilute

He suggested doing the above before adding any more chemicals. Do you think this is a sensible approach?

Many thanks!
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Wacky Pool readings

Postby Denniswiseman » Tue 30 Sep, 2014 05:36


The chlorine level will reduce itself naturally
The TA can be reduced with Muriatic Acid (Hydrochloric acid)
You would then have to aerate to raise the PH as the acid reduces the PH as well
The Cyanuric acid isn't that high but a partial drain down and refill will get it down (you may have to repeat this)

The partial drain and refill would seem to be the best to start with but be carefull not to drain to much in one go as it could affect your liner. I would suggest about a foot

Wacky Pool readings

Postby Timothy_S » Mon 17 Nov, 2014 07:16

pH and Chlorine values for good water quality

The pH is a measure of the acidity of the water. The pH scale goes from 0 to 14, where pH 7 is neutral. If the pH is above 7, the water is basic; if it is below 7 the water is acid. The optimum pH for pool water is 7.4, since this is the same as the pH in human eyes and mucous membranes. A pH of 7.4 also gives good chlorine disinfection.

A low pH gives:
- aggressive water, which damages the mechanical components of the pool
- irritations of the eyes and mucous membranes
- damage to the pool liner

A high pH gives:
- poorer chlorine disinfection
- skin irritation
- lime precipitation
- cloudiness

The guideline pH figure is 7.2 – 7.6.

To lower the pH, use sodium bisulphate; to raise it use sodium carbonate.


Chlorine compounds may provide organic or inorganic chlorine. Organic chlorine is trichlorisocyanuric acid (for weekly chlorination) and dichlorisocyanuric acid (dissolves rapidly and is suitable for small pools).
Inorganic chlorine is calcium hypochlorite (for daily and shock chlorination) and sodium hypochlorite (liquid).

When a pool is dosed with either organic or inorganic chlorine it is free chlorine that attacks bacteria and
contaminants. As the chlorine acts it is converted into combined chlorine. Combined chlorine (also known as
chloramines) is ineffective, smells of chlorine and may cause irritation of the eyes and mucous membranes. To reduce the combined chlorine, the pool is shock chlorinated with calcium hypochlorite. The high chlorine content that forms
temporarily on shock chlorination disappears quite quickly in an outdoor pool, but can also be lowered with chlorine reduction compounds. Chlorine is continuously consumed in the pool, and different factors determine the chlorine consumption, including bathing frequency, water temperature, sunlight and pool size. A test kit is used to measure the chlorine content. Most kits measure free chlorine, but to measure the combined chlorine you need to measure total chlorine. Total chlorine is the sum of free and combined chlorine.

If organic chlorine (weekly chlorination) is used, cyanuric acid accumulates in the pool. Where the cyanuric acid content is above 100 ppm (mg/l), chlorine blocking may occur, making the chlorine ineffective. Cyanuric acid can be removed by adding water from the mains supply.

Cyanuric acid acts as a chlorine stabilizer, preventing the sunlight from breaking down the chlorine, for example.
It is therefore advisable for outdoor pools to have a cyanuric acid level of 10-20 ppm (mg/l).

Guideline values:
Free chlorine: 0.5-1.5 ppm (mg/l)
Combined chlorine: 0-0.5 ppm (mg/l)
Total chlorine: 0.5-1.5 ppm (mg/l)
Cyanuric acid: 0-20 ppm (mg/l)

http://www.wikihow.com/Properly-Maintai ... -Chemistry

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