How much chlorine is too much before closing?

[Sbcmurphy]

Hi all. I had a trouble free first summer of pool ownership thanks to this forum - clear water, no algae and a newfound understanding of chemistry.

Then 3 days before closing I noticed a small green stain in the deep end. I went a little heavy handed and brought chlorine up to about 27ppm on CYA of 40ish. A company is coming later today to blow the lines and close it up.

Can I add another jug of chlorine to help control the potential algae? It would bring me up to about 35ppm before the cover goes on.

Are there significant drawbacks to this in a vinyl pool with no heater or SWG?

 

[ajw22]

Bringing your FC up above SLAM FC level risks bleaching out the color in your liner.

For CYA 40 SLAM FC is 16. 27 ppm is plenty. No reason to add more.

You should consider adding Polyquat 60 which lasts longer in a closed pool then chlorine...

Algaecide - Further Reading

www.troublefreepool.com

How To Use Polyquat 60

The following is Buckman Labs’ recommendation on how to use Polyquat 60 for closing your pool for the season.

As they recommend for proper winterization, the pool should be "shocked" with about 5-10ppm chlorine to destroy any lingering oxidant demand and remove any residual ammonia or chloramine, etc. After a couple of days, adjust the pH back to 7.2-7.6 and then add Polyquat 60 at the maximum rate as instructed per the label. This approach allows you to receive the highest benefit from both chemicals.

Note that Polyquat and linear quat algaecides are organic compounds that are known to cause interference's with certain color indicating reagents like pH indicators. Adjust the pH before adding Polyquat 60 and there is no reason to test pH after adding it.

Another point that they make regarding using this algaecide in pool water is that after the addition of Polyquat 60, it’s important to keep the circulation pump on for at least 24 hours to make sure that the algaecide is thoroughly distributed throughout the pool.

If you raise your water to SLAM FC level then you should let the FC drift down before adding Polyquat 60. Having a moderately higher level (½ SLAM level so the FC/CYA ratio of 20%) is okay as well. The idea is that the Polyquat should last through the winter even if the chlorine does not.[

Buckman Labs says that even if the Polyquat is broken down, it is still effective when used as an algaecide. Moderate to high levels of chlorine break down Polyquat but it still only transforms the formula into shorter chain polymers that are still just as effective.