FC consumption when closing with Algaecide


LifeTime Supporter
Jul 31, 2013
Staten Island, NY
I believe I've read on the forum that chlorine will break down algaecide (polyquat). When using algaecide during pool closing, won't the pool consume more FC than if you had not used algaecide maybe to the point of total FC consumption well before opening? At the very least, wouldn't the chlorine break down all the algaecide negating any benefit of its use leaving you with much lower levels of FC?

Last closing was my first and I did use polyquat. I opened to crystal clear water with a residual FC of 2 and no CC. I guess I can just repeat but wanted to educate myself first.




Well-known member
Jun 22, 2013
East TN
Yes, chlorine will break down polyquat and quat algaecides. I believe there is an added benefit of having the polyquat turn into a clarifier when broken down (If I remember right). If you opened to clear water then you done a good job and just repeat. My only suggestion is keep a check on your FC a few times during the closing especially about spring time.

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
San Rafael, CA USA
Buckman Labs says that the Polyquat that is broken down is still effective as an algaecide. Also, if you close the pool with the water temperature cold (50ºF or below), then the algaecide will last a much longer time even in the presence of chlorine. That's the recommended approach. Basically, at warm pool temperatures in one week the Polyquat might degrade by at about one-third with normal chlorine levels, but at 50ºF it would take perhaps 5-7 weeks for that same level of degradation to occur. So if you close late enough and open early enough, you could have the algaecide and even the chlorine still have some residual when you open in spring.