adding javel over the winter

[osie]

Hi All

Until this year I have set up the pool for winter and put a few galets in there which seem to stay in there all winter.  I have assumed that they have some use even though they reduce very slowly.

In a bid to convert to jave and reduce CYAl, I would like to know what quantity and  how often I would need to add this.

Can I just add a few litres now and turn the pump for a few hours and then leave it till march, or do I need to do regular additions as there is no stabilizer, or maybe you dont need javel over the winter at all?

Thanks in advance

Osie

[Théière]

Morning Osie,

You'll have to refresh my memory, is your pool covered over winter and how big is your pool in m3. What is your current CYA level?

 

[osie]

Hi Teapot

The pool is not covered..

It is about 80m3 and the CYA was 0.7 in September... done by DASS.  I do not yet have a CYA reader.

Thanks

Osie

[Théière]

Without a cover you need regular additions, just like normal running.  Just as the gallets dissolve slowly because the water is cooler and CYA takes an age to dissolve. that does also mean the amount of chlorine dissolving into the water is also tiny. Multiactions usually contain copper which helps keep the algae away. 400ml of 9.6% javel would give you 0.5ppm how long that would last is any one's guess.

What units were the DDASS using 0.7%, mg/litre, ppm?

[osie]

The 70 would have been 70mg... It was the maximum normal tolerance allowed.

The pool is always frozen over in the winter and I have never had a problem with water colour.  In fact I would not be able to add javel unless I make a hole in the ice.

[Théière]

Where did my post go?

Ok, let's try again. If the pool is in a cold region then there isn't so much to worry about as algae won't grow if the temp drops below about 10 deg so just adding some and mixing before it gets too cold should be sufficient. I would still be tempted to at least buy a bache to cover over to stop dirt and sunlight from entering and risking any growth whilst chlorine is low. Some people have reported their CYA figures dropping drastically after a freeze which could be down to a bacteria consuming it and converting it into ammonia.

[osie]

That sounds good news... the time the motor is not running is just the few months the water is frozen over...

I keep considering a bache.. will one day go ahead and get one.

Maybe a silly question but , is it not a good idea that the CYA goes right down so that you can build it up again next year with the gallets?

I guess that a low CYA is a good way to start the pool opening?

p.s. Thanks for all the good answers!!

[Théière]

It would be very handy having the CYA drop via bacteria if it wasn't that it gets converted into ammonia which has an enormous capacity to consume chlorine before it gets converted to monochloramine or oxidised out of the pool, so in short it's bad.

The other problem starting off low in CYA is you loose your chlorine in a couple of hours so that cost's a lot more before the CYA gets built up again to a good level unless you add the CYA manually by dissolving it in front of the skimmer.

[osie]

I was sure life is not as easy as I was hoping :-)

[chem geek]

There is a slow oxidation of CYA by chlorine so over months the loss of CYA can be noticeable, but this is on the order of 2-3 ppm CYA per month during the warmer pool water in the summer.  Some people report higher losses of around 5 ppm CYA per month and that is also the typical rate of loss in hot spas (say, using the Dichlor-then-bleach method).  As for winter losses, most people who maintain chlorine in the water don't find a loss beyond that explained by water dilution from rain overflow, but some report an additional loss.  For those who let their pool go over the winter (i.e. let the chlorine level get to zero at some point), anaerobic bacteria can grow and consume the CYA and either convert it to ammonia creating a HUGE chlorine demand upon spring opening where every 10 ppm CYA loss can create 30 ppm FC demand or additional bacteria can use the ammonia and convert it to either nitrates or to nitrogen gas.  This is described in more detail in this thread.

Unfortunately, there is no easy way to force the bacteria to do what one might want such as oxidizing the CYA to nitrogen gas and carbon dioxide gas.  If there were, then that would be a way to reduce CYA levels.  As you pointed out, life is not as easy as one might hope.

[osie]

Well all that info is great to know that there is reason to keeping chlorine levels up in the winter.  It is not just a waste of money.

Thanks to both of you for filling some of the knowledge gaps.