Can't get rid of algae

Chlorinating, maintaining the right chlorine levels, chlorine problems. Dichlor, trichlor, cal hypo, bleach, granules, chlorine pucks or sticks.

Can't get rid of algae

Postby davethepoolguy » Thu 02 Jun, 2011 17:14

I maintain about 15 pools a week. I have been doing this for years. Starting last year, I noticed that I was getting algae in pools even though the chlorine was high. The chemicals are all balanced properly but this is now happening in 5-6 different pools. I believe the problem to be either in the tri-chlor or the calhypo. Can anyone shed some light on what is causing it and/or how to fix it. any help would be greatly appreciated.
davethepoolguy
 

Can't get rid of algae

Postby chem geek » Fri 03 Jun, 2011 00:37

There is no mystery here. The following are chemical facts that are independent of product concentration or of pool size:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

So even with a typical 2 ppm FC per day chlorine usage, having only Trichlor as your chlorine source would result in an increase in CYA of over 2*30*0.61 = 36 ppm PER MONTH. Higher CYA levels reduce the active chlorine level requiring a proportionately higher FC level to prevent algae growth. In manually dosed pools, if you don't have the FC level be at least 7.5% of the CYA level, then algae can grow faster than chlorine can kill it. See the Pool School for more information.
chem geek
Pool Industry Leader
Pool Industry Leader
 
Posts: 2353
Joined: June 2007
Location: San Rafael, California

Can't get rid of algae

Postby davethepoolguy » Fri 03 Jun, 2011 07:38

Makes sense. Most of the Pools I recently took over and they were using dichlor and trichlor tabs. I guessing the only way to fix it is drain the pools. I drained approx 2/3 of the water from one and changed the sand. It had no noticeable affect on the chlorine levels. I never used to have this problem. Any chance that the manufacturer's of chlorine have increased the level of cya as maybe a cost cutting measure or something. I hear I'm not the only one having this problem lately. BTW, all the pools are vinyl and located in central AL.
davethepoolguy
 

Can't get rid of algae

Postby chem geek » Fri 03 Jun, 2011 21:00

Dilution of the pool water is the only way to lower the CYA though sometimes you get lucky and it drops over the winter (which may or may not convert to ammonia creating a huge chlorine demand).

No, nothing has changed -- Trichlor and Dichlor always follow the rules I gave since they are related to the chemistry and not concentration of product. Perhaps there was less winter and summer rain overflow that in past years might have diluted the water more. Or perhaps more algae nutrients (phosphates and nitrates) have accumulated in the pools.

To prevent algae growth, you've got several choices. The most straightforward and least expensive is to use unstabilized chlorine such as chlorinating liquid or bleach and maintain the appropriate FC/CYA ratio. However, this requires adding chlorine every day or two unless you have a mostly opaque pool cover in which case you can add it perhaps twice a week. You can automatically dose by using The Liquidator or a peristaltic pump or a saltwater chlorine generator. With these techniques, you should not need any regular shocking of the pool.

If you are willing to spend more money and can only service your pools weekly, then you can have Trichlor in a floating feeder or inline chlorinator and use a weekly algaecide such as PolyQuat 60 or you can use a phosphate remover (doesn't work as well if the pool is high in organic phosphates) or add 50 ppm Borates (boric acid) to the pool. You could use a copper-based algaecide, but that can stain pool surfaces and turn blond hair greenish.
chem geek
Pool Industry Leader
Pool Industry Leader
 
Posts: 2353
Joined: June 2007
Location: San Rafael, California

Can't get rid of algae

Postby davethepoolguy » Sat 04 Jun, 2011 06:35

thanks for the help.
davethepoolguy
 

[Show] Post a reply


Return to Chlorine


Pool Maintenance   •   Pool Wizard   •   Pool Help   •   Havuz Bakımı