Shocking A Covered Pool?

[Don]

Hey gang,

As mentioned in another thread, I currently have my pool covered with a micro mesh cover, and have left it running.

I have a Rainbow Chlorinator, and keep chlorine tabs in it. Even at the lower setting, my chlorine alway sseems to stay up around the 5 range.

Back prior to covering, I would always vacuum , shock, and put algae bomb in my pool once a week.

Now that it is colder, and covered, I am just wondering on thoughts of how often to shock a pool? I do keep a check on my water chemistry, to make sure it does not get out of whack, just wondering how often I should go ahead and shock it, and put algaecide in it, with it covered up?

Thanks for any tips,

[chem geek]

If you maintain chlorine in the pool with an FC level sufficiently high for the CYA level, then you should not need to shock the pool -- not just during closing but during the summer as well. Also, if the water gets colder, especially 55ºF or below, then algae growth will be very slow. See the Pool School for more info.

[Don]

Sounds good, thanks for the reply and the link!

[Beelzy]

Be careful not to run that chlorine level too high, you could wind up with metal staining.

[chem geek]

It is high pH that leads to metal staining, not high FC. Yes, for iron solid metal and ferrous iron in the water it is when it gets oxidized by chlorine to ferric ion that it can then stain, but this happens even with low levels of chlorine. When one shocks the pool with higher levels of FC, it is the use of hypochlorite sources of chlorine that raises the pH upon addition that causes the staining, not the high FC itself. So maintaining a higher FC when the CYA is higher, but properly managing the pH keeping it from getting too high will not lead to metal staining.

Also, when the CYA is higher, a high FC does not result in higher active chlorine (hypochlorous acid) concentrations and it is active chlorine that oxidizes solid iron to ferrous ion and ferrous ion to ferric ion. Basically, different levels of FC and CYA that have the same FC/CYA ratio have roughly the same active chlorine (hypochlorus acid) level, assuming the pH is the same.

[quantumchromodynamics]

The need to shock a pool arises when the dead chlorine overpowers the good. So you wouldn't need to shock more than twice a year unless your pool is completely neglected which is why many residential pools carry out the process very often.

What is "dead" chlorine?

[Don]

Thanks, I removed the mesh cover yesterday as the leaves have all pretty much fallen, will certainly be keeping an eye on the water balance now.

[Don]

The need to shock a pool arises when the dead chlorine overpowers the good. So you wouldn't need to shock more than twice a year unless your pool is completely neglected which is why many residential pools carry out the process very often.

This is interesting, I was always under the impression you should shock a pool like once a week during the swimming season.

I take care in keeping the water balanced, sounds like I do not need to shock so much...

[chem geek]

Regular shocking is not needed if the Free Chlorine (FC) level is properly maintained relative to the Cyanuric Acid (CYA) level. For a non-SWG pool, this means that the FC should be around 7.5% of the CYA level. For an SWG pool, the FC can be around 5% of the CYA level. This assumes one is not using any supplemental algaecides as these are not necessary if one maintains these FC/CYA levels.

[Don]

Thanks for the info - btw, what is SWG ?

[chem geek]

Saltwater chlorine generator. A pool that has higher salt levels with a device that makes chlorine from that salt (from electrolysis).

[Don]

Ah ok thanks, mine is not SWG.