Green water

Algae problems in swimming pool water.
Green (cloudy) water or slimy pool walls.
Black algae. Mustard algae. Pink or white pool mold.
jamesdal1
Pool Newbie
Pool Newbie
Posts: 3
Joined: Wed 20 May, 2009 15:05
My Pool: 13,500G, In Ground pool, Carthridge filter Haywood
Location: Dallas, TX

Green water

Postby jamesdal1 » Wed 20 May, 2009 15:49

Problem: Green water

FC: 0
TC: -
pH: 8.0
TA: 80
CH: 200
CYA: 40

My pool: 13,500 gallon
Pool chemicals: chlorine tablets, muriatic acid, soda ash, phos free, alkalinity up
My pump & filter: Hayward SwimClear cartridge filter series
Other info: Cleaned carthridge 4 days ago.

I can't get the green water out, I had a pool company come out and quote me $300 for 6 hours of work, they didn't even get a water sample.

I just shocked my pool with 2 pounds of power powder plus and added 12 ounces of muriatic acid, any suggestions?


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

Green water

Postby chem geek » Wed 20 May, 2009 21:18

If it's algae, follow Defeating Algae . If it's a clear green, then it could be copper and you should have the pool water tested for that. With high pH and zero chlorine, it could be either, but if it's cloudy green or you can see visible algae, then it's algae.
jamesdal1
Pool Newbie
Pool Newbie
Posts: 3
Joined: Wed 20 May, 2009 15:05
My Pool: 13,500G, In Ground pool, Carthridge filter Haywood
Location: Dallas, TX

Green water

Postby jamesdal1 » Wed 20 May, 2009 22:35

what do you mean by by clear green? by clear, i can't see the bottom, its green, can only see the first stair.
maidscene
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Posts: 1
Joined: Thu 21 May, 2009 01:24
My Pool: filter and pump repairs, weekly and chemical services, etc...
Location: Arizona

Green water

Postby maidscene » Thu 21 May, 2009 02:06

i've been finding a lot of pools this past week that are having trouble clearing up. "Usually the shocking will do the trick" they say. Yea, that is typically true, but not this season. So far this week 3 out of 3 pools had HIGH PHOSPHATES. Test Phosphate levels first. 125ppb or less is ok. If higher, get some sort of Phosphate remover (may different brands are made), add according to directions. Run 24hrs, backwash filter, or clean cartridges. Then add some Clearex 500 to clear up the cloudy water. Continue running pump until water clears (about 24hrs).


recap:

Phospates wont let the chlorine kill algae. So let's get rid of those phosphates and then shock it.


don't forget the stabilizer (cynauric acid), it helps prevent chlorine loss due to the suns intense UVs.
MaidScene Pool Services
Michael Nelson
www.MaidSceneServices.com
chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Green water

Postby chem geek » Thu 21 May, 2009 14:12

I'm sorry, but this is not exactly true. My pool has 2000-3000 ppb phosphates and I not only keep algae from growing, but when I opened this season I let the chlorine drop to zero by mistake and an algae bloom started (water got cloudy) and also bacteria converted some CYA into ammonia. This took a LOT of chlorine to get rid of, but it is not true that phosphates prevent chlorine from killing algae or bacteria. I was able to get past it and the pool is clear and fine now.

Phosphates (and nitrates) are algae food so they can grow if they are present. That does NOT mean chlorine cannot kill that algae. However, you have to shock with a Free Chlorine (FC) that is sufficiently high and a level that is 40% of the Cyanuric Acid (CYA) level is good enough for clearing a pool reasonably quickly.

So you need to look at phosphate removers similar to algaecides (e.g. PolyQuat 60 weekly). They prevent algae growth (at extra cost), but they are NOT necessary if you maintain a proper chlorine level relative to the CYA level. For a manually dosed pool, one should target a minimum FC that is 7.5% of the CYA level. If one lets the FC drop below around 5% of the CYA level then algae can grow faster than the chlorine can kill it and this is assuming worst-case high phosphate levels. Algae under the most ideal conditions are still limited in how fast they can grow since sunlight is still limited in its intensity. Algae double in population every 3-8 hours. Chlorine can definitely kill it quickly enough IF the FC/CYA ratio is sufficient. So look at phosphate removers and algaecides as insurance if you don't think you can maintain a sufficient FC/CYA ratio.

Double check the CYA levels in the pools that caused you problems. Was the FC level in such pool consistently maintained at least at 5% or more of the CYA level, preferably 7.5% of the CYA level or higher? If not, then that explains what happened. Continued use of stabilized chlorine (Trichlor, Dichlor) increase the CYA level rather quickly due to the following chemical rules (including one for Cal-Hypo, just for completeness):

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 7 ppm.

Also, shocking the pool does not mean just dumping some chlorine in and seeing what happens. It means checking the FC level within an hour and if it's low, raise it to shock level and keep doing this to MAINTAIN the shock level of chlorine. The rate of FC drop will get slower over time until all the algae is killed and cleared. The pump should be kept on, brushing should be done to stir up the algae to get it filtered out more quickly, and the filter should be cleaned/backwashed.

For more details, see the Pool School.

Richard

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