What would happen with very low cya and only adding bleach in evening ?

Jul 10, 2016
College Station
It is well known that chlorine is much more effective when cya is low.

What would happen say if cya were 0 and fc raised to say 1.0 each evening using bleach after sun went down ? The lack of cya would make the chlorine very effective overnight, during day sun would rapidly drop fc.

would algae even have chance to get to high levels during day before adding bleach again at night ?


Mod Squad
LifeTime Supporter
Jul 10, 2012
Tallahassee, FL
What state is College Station in?

With a CYA of 0 and FC put up to 1.0 the sun will eat the FC way before the day ends giving algae a chance to get started. If you are in a sunny, hot state it will happen much faster.

Algae does not need to get to high levels. It just needs a toe hold. It goes from there. A little at a time until BOOM you have a algae bloom :(



TFP Expert
LifeTime Supporter
In The Industry
Jun 12, 2009
NW Ohio
You will end up with zero FC before noon. Algae would grow, then you would add 1 FC that evening and it wouldn't be enough to kill all the algae. After a couple days your pool would be green. On top of that with zero FC in your pool in the afternoon you would have no protection against various bacteria and viruses that might be transmitted through the water. Also with nothing to buffer the chlorine as you add it you will likely see parts of your plaster fade over time where you add the chlorine.

And if you do this but decide to add additional chlorine before swimming to assure the water is sanitary, well first you just doubled your work. Second, 1 ppm FC in a pH of 7.5 is about 8 times stronger than the following the FC/CYA ratio we use here. So it would be less comfortable, create more CC's so would smell like your typical chlorine pool, and fade bathing suits.

All in all, I can't think of a single positive aspect to the method you describe.