Baffled!!

[French Riviera]

Hi All, I'm new to this forum and would greatly appreciate any help that can be offered on this problem.
I am not new to pool maintenance and in the past have generally been able to overcome any issues but this one has me stumped.
I have an 84 cubic metre inground pool with retractable floating cover. The pool temperature at present is around 12°C and the water is clear as most of the time the cover is in the closed position.
I have a pH reading of 7.4, I have a TA reading of 85, a CYA reading of 56. It is a straightforward chlor pool, I tend to use Hypochlorite sticks most the year, liquid chlor at times and just put in blocks when I need to up the CYA. The issue is that I can literally pour in 10 litres of liquid chlor and, within 20 minutes, the pool will show Zero chlor. There is no algae present in the pool, nothing I can see that would be eating it. Phosphate levels are in check, I don't get much debris in the pool due to the cover. Any ideas what could be causing this? Could the cover being closed most the time be creating a problem?
Any ideas / help would be greatly appreciated, thanks in advance.

 

[ajw22]

Welcome to TFP.

Do a Overnight Chlorine Loss Test. If you fail it, which sounds like you will, then follow the SLAM Process

You can have algae that is unseen consuming your chlorine.

What is the % strength of the liquid chlorine being used and how old is it?

Breakdown of Bleach Over Time by Storage Temp - Further Reading

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[Bperry]

Hi All, I'm new to this forum and would greatly appreciate any help that can be offered on this problem.
I am not new to pool maintenance and in the past have generally been able to overcome any issues but this one has me stumped.
I have an 84 cubic metre inground pool with retractable floating cover. The pool temperature at present is around 12°C and the water is clear as most of the time the cover is in the closed position.
I have a pH reading of 7.4, I have a TA reading of 85, a CYA reading of 56. It is a straightforward chlor pool, I tend to use Hypochlorite sticks most the year, liquid chlor at times and just put in blocks when I need to up the CYA. The issue is that I can literally pour in 10 litres of liquid chlor and, within 20 minutes, the pool will show Zero chlor. There is no algae present in the pool, nothing I can see that would be eating it. Phosphate levels are in check, I don't get much debris in the pool due to the cover. Any ideas what could be causing this? Could the cover being closed most the time be creating a problem?
Any ideas / help would be greatly appreciated, thanks in advance.

How are you testing the water?

 

[ajw22]

How are you testing the water?

Being in France, no way you will approve of it.

 

[French Riviera]

Hi, thanks for all the input. To answer a few questions, haven't yet read the "slam test" bit, will do so. Having put 10 litres of 36° Liquid chlor, bought that day from the store on two occasions, plus having shocked a month ago with sodium hypochlorite shock, I would be surprised if there was much lurking algae wise? The water looks good.
I use a pool lab 101 photometer to get my readings and also a simple little drip tester. The TA was low (37) but I raised it (85) and then balanced the pH. This absence of chlor has gone on for a few months now, tried both Hypo sticks and alternated with some regular multi function chlor blocks. Nothing seems to show up. Worrying now with season approaching and water temperature rising!

 

[ajw22]

Your lack of chlorine is either:

• Bad testing
• Algae consuming the chlorine
• UV consuming chlorine
• Low to no % chlorine in the chemical added.

Create a solution using your liquid chlorine and distilled water to test your chemical and testing method.

To test the % of sodium hypochlorite in liquid chlorine:

1. Add 1mL of the LC to 100mL of distilled water.
2. Swirl to mix.
3. Add 1mL of the resulting mixture to 100mL of fresh distilled water.
4. Swirl to mix.
5. Use your Pool Lab 101 to get the resulting ppm’s of FC. The number of ppm’s is roughly equivalent to the chlorine percentage.

Use distilled water only and do the test immediately. There’s no need to do extensive mixing.

The proper way to make a dilution is to use a well calibrated flask, fill it 2/3rds with distilled water, add the volume of chemical you are diluting and then fill the flask up to mark with distilled water. Then swirl for 30secs or so to mix. Erlenmeyer flasks are the appropriate glassware for the task.

 

[ajw22]

Pool Lab 101 only tests 0 to 8 ppm of chlorine.

PoolLab.org - official website | Water-i.d. GmbH

Official PoolLab 1.0 website |The PoolLab® 1.0 is a triple wavelength photometer for professional water analysis of private pools and spas.

poollab.org

What does it read if your chlorine is very high?