Does chlorine attack covers?

[Durk]

I was in my FLPS refilling my LC carboy and looked at the closing display. Big red-lettered signs were warning people "DO NOT USE CHLORINE TO CLOSE YOUR POOL--IT WILL DESTROY YOUR COVER".

I have used BBB sans borates in the summer for a few years now, but I have closed since 2005 using either the Anthony&Sylvan (my PB) or the InTheSwim non-chlorine closing chemical kits. These are pretty much identical, 3lbs. of MPS shock and an 'oxidizer' floater, plus some foam absorber gadget. I have had excellent results since 2005 (I let PB close the first year in case there were any problems and so I could see what he did.) I open to clear water and a clean pool, barely needs a vacuum.

I have been planning to switch to the TFP closing chlorine technique this year. I would appreciate any comments on the cover issue or non-chlorine closing in general. I have a healthy level of skepticism regarding pool stores but the issue does concern me. Thanks.

 

[duraleigh]

How much chlorine?

Would 1ppm destroy your cover? Uh-oh, then you can't fill the pool from tap water.

Their sign is absurd. Sort of like,

"DO NOT EAT TOO MUCH LETTUCE, IT WILL KILL you"

(Those of you that haven't died yet have simply not eaten too much)

 

[Durk]

How much chlorine?

Would 1ppm destroy your cover? Uh-oh, then you can't fill the pool from tap water.

Their sign is absurd. Sort of like,

"DO NOT EAT TOO MUCH LETTUCE, IT WILL KILL you"

(Those of you that haven't died yet have simply not eaten too much)

Not to be rude, but welcome to the absurd argument club. The 1 ppm from tap water is not going to be there all winter any more, and certainly less, than all the LC I put in all summer. I actually agree with your conclusion, but you didn't help your case, there. Certainly pool level FC attacks plastics in general to some degree, straps on pool toys left in the pool degrade more than ones just left in the sun.

 

[chem geek]

Chlorine is an oxidizer and will degrade some forms of plastic. Clearly one can have plastics that are chemical resistant such as those used to hold bleach, chlorinating liquid and Muriatic Acid, but such bottles are hard plastic. The chemicals that tend to make plastic more pliable and soft, such as used for pool covers, also unfortunately tend to make them more susceptible to breakdown from chlorine as well as from the UV in sunlight. That's just the way it is.

With CYA in the water, the chlorine strength is moderated. The shock level of chlorine with an FC that is around 40% of the CYA level is equivalent to 0.6 ppm FC with no CYA or roughly 4 to 10 times the level in a typical manually dosed chlorine pool with an FC from 7.5% to 15% of the CYA level that is equivalent to around 0.06 to 0.14 ppm FC with no CYA. So during the earlier part of the closing, the rate of destruction of the cover from chlorine will be faster and will slow down as the chlorine level drops over the winter. However, keep in mind that cover destruction only partly comes from chlorine and also comes from sunlight.

In theory, using PolyQuat 60 for closing by shocking first and then adding PolyQuat 60 (which will lower the chlorine level) would be less harsh, but it probably won't last through the winter either. If one is able to add chlorine at times during the winter, that would be preferable, but some form of mixing or circulation would be needed to ensure thorough mixing.