Filtration hours - daylight

Algae problems in swimming pool water.
Green (cloudy) water or slimy pool walls.
Black algae. Mustard algae. Pink or white pool mold.
AZ Dry Heat
Pool Newbie
Pool Newbie
Posts: 2
Joined: Thu 01 May, 2008 17:10
Location: Phoenix, Arizona

Filtration hours - daylight

Postby AZ Dry Heat » Thu 01 May, 2008 18:06

Hi all,

I just registered for this forum to hopefully provide and receive help on various pool issues. I've had a pool for 8 years in the Phoenix area and have learned some good lessons along the way, but there are still many unknowns to me.

I read that algae grows much worse if the pump/filter is not running during the daylight hours, when algae can grow. I use a time-of-use plan for my electricity, where from May-October the power cost is much higher between 1-8 pm. Given that, I don't like to run the pump then. The trade-off may be the cost of additional chlorine, algaecide, etc.

Do you think that not running the pump during those sunny hours has a significant effect on algae growth? I run the pump for 10-11 hours/day in the summer, where it gets HOT here. Thanks!

chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Postby chem geek » Fri 02 May, 2008 13:38

If the pump isn't running, then localized growth of algae can end lowering the chlorine concentration in that area to the point where the algae can grow more quickly. Think of the process as competing rates where the algae tries to grow and the chlorine tries to prevent such growth. When the rate of killing of the algae by chlorine is faster than the rate of growth by the algae, then the algae is kept away. So good circulation helps make sure that the chlorine level stays up even in areas of nascent algae growth.

However, the most important factor is to maintain a Free Chlorine (FC) level that is at least 7.5% of the Cyanuric Acid (CYA) level (10% is a decent target). Chlorine's effectiveness is reduced by the CYA level and in fact is proportional to the FC/CYA ratio so when CYA goes up you need to raise the FC accordingly. Another alternative is to use a weekly algaecide such as PolyQuat 60 or a phosphate remover.

Just keep in mind that stabilized sources of chlorine add to the CYA level and CYA only gets reduced by dilution -- it generally builds up quickly. For every 10 ppm FC added by Trichlor tabs/pucks, they also add 6 ppm to CYA. For every 10 ppm FC added by Dichlor powder/granules, it also adds 9 ppm to CYA.


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