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Pool turns green when adding granular chlorine - Swimming Pool Help

Pool turns green when adding granular chlorine

Algae problems in swimming pool water. Green (cloudy) water or slimy pool walls. Black algae. Mustard algae. Pink or white pool mold.

Pool turns green when adding granular chlorine

Postby Pool User » Mon 02 Nov, 2009 16:16

Hi Guys,

Had a rough first day. cleaned my first pool. I tested the water and discovered it had no chlorine, no or little PH reading and zero alkalinity.

I added granular chlorine and the pool turned green. I then ran out and bought PH and Alkalinity increaser hoping this would clear the green away but it is still green. why?
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Pool turns green when adding granular chlorine

Postby brad s » Tue 03 Nov, 2009 10:19

How did you test the water? What do you mean by little or no pH? Was the water clear before you added the chlorine? How soon did it turn green?
brad s
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Pool turns green when adding granular chlorine

Postby Pool User » Tue 03 Nov, 2009 11:06

If the water is clear and sparkly green then you have copper. Add more chlorine to oxidize it and it usually goes away.
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Pool turns green when adding granular chlorine

Postby brad s » Tue 03 Nov, 2009 11:12

Or it could be iron. The reddish iron color against a blue liner makes green. The chlorine most likely oxidized the dissolved metals. If you have a sand filter, it should clear on its own. The metal will percipitate out and get filtered. The next time you backwash, you should see a dark orangish colored water come out the backwash line.
brad s
Pool Enthusiast
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Posts: 10
Joined: August 2009
My Pool: 14,000 gal kidney
3/4 HP hayward super pump, Pentair IC-40 SWCG, Aquacomfort heat pump.

Pool turns green when adding granular chlorine

Postby Pool User » Tue 03 Nov, 2009 17:18

the water is worst today. it has green granular type sand everywhere on the bottom. the water is kinda murky green and there is a layer like an oil slick on the surface in some areas. almost looks like scales or some sort.

thanks for the replies guys its much appreciated.

any thoughts on this? I was thinking it could be metal but the water would be clearer I think.

this is my first pool and I've messed it up. the pool was clear (however no chlorine in it and ph and alk was almost non existent so water wasn't healthy) but now it looks awful (although the chlorine is up around 4 now). I might get fired soon...lose my first pool. :(
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Pool turns green when adding granular chlorine

Postby chem geek » Wed 04 Nov, 2009 00:09

If you add a hypochorite source of chlorine and the pool turns color almost right away, then that isn't algae but is metals precipitating out of solution at least partly due to the increasing pH since adding a hypochlorite source of chlorine increases pH upon addition. If you then increased the pH further, you just made the problem even worse. Adding acid to lower the pH would have at least put some of the metal back into solution after which point you could add a metal sequestrant to prevent it coming out again.

Has this pool used copper-based algaecides? Or did it use Trichlor pucks in the skimmer perhaps? The former would add copper to the pool and the latter would make the pool very acidic. Zero TA means the pH is below 4.5 which is quite low. So perhaps copper from the heat exchanger got dissolved.

The earlier post about adding more chlorine clearing up copper won't work. Chlorine is great for clearing up algae, but it won't fix a metal problem.
chem geek
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Pool turns green when adding granular chlorine

Postby Pool User » Wed 04 Nov, 2009 14:55

chem geek wrote:If you add a hypochorite source of chlorine and the pool turns color almost right away, then that isn't algae but is metals precipitating out of solution at least partly due to the increasing pH since adding a hypochlorite source of chlorine increases pH upon addition. If you then increased the pH further, you just made the problem even worse. Adding acid to lower the pH would have at least put some of the metal back into solution after which point you could add a metal sequestrant to prevent it coming out again.

Has this pool used copper-based algaecides? Or did it use Trichlor pucks in the skimmer perhaps? The former would add copper to the pool and the latter would make the pool very acidic. Zero TA means the pH is below 4.5 which is quite low. So perhaps copper from the heat exchanger got dissolved.

The earlier post about adding more chlorine clearing up copper won't work. Chlorine is great for clearing up algae, but it won't fix a metal problem.


thanks for the reply. this pool is in the Bahamas.

I had another pool company come round to check. I used to work with the owner. they said the alk was so high it read clear. the PH was still under 6.8. the chl was 4-5. also found out the stuff floating on the surface was paint. apparently the pool was painted. why? I have no idea as it is a gunite pool. but now I owe $250 for the visit and this will include a filter strip down and clean. plus they said they have to balance the pool and strip and clean the filter every week. that will cost me $150 per week until the paint it out of the system. now I wonder do I have to drain and repaint the pool?

what on earth do I do? I should have stayed at teaching guitar!
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Pool turns green when adding granular chlorine

Postby chem geek » Thu 05 Nov, 2009 02:54

I can find nothing about high TA resulting in a clear solution. Are you using test strips? What kind of test kit are you using? I assumed you were using a good test kit such as the drop-based Taylor K-2006 shown here. The TA test normally goes from green to red so if initially red then that's a TA of zero and a pH below 4.5 which is what I thought you were describing. At high halogen levels, the TA test can go from blue to yellow, but it shouldn't be clear.

Others will have to comment on the paint.
chem geek
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Pool turns green when adding granular chlorine

Postby Pool User » Thu 05 Nov, 2009 08:14

chem geek wrote:I can find nothing about high TA resulting in a clear solution. Are you using test strips? What kind of test kit are you using? I assumed you were using a good test kit such as the drop-based Taylor K-2006 shown here. The TA test normally goes from green to red so if initially red then that's a TA of zero and a pH below 4.5 which is what I thought you were describing. At high halogen levels, the TA test can go from blue to yellow, but it shouldn't be clear.

Others will have to comment on the paint.


Thanks. I have a Guardex pool test kit. I couldn't find a Taylor kit on the island. everyone was out of them that carry them.

The TA test just wouldn't change color when I added the 5 drops. it just stayed clear. I was told by another pool guy who came there that the TA was actually high and not low. so now I might have a high TA, low PH (didn't seem to go up when I added PH booster) and a chlorine of 4-5. the water is green with green sand like stuff on the bottom and some sort of oil like scale stuff floating on the surface.
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Pool turns green when adding granular chlorine

Postby Pool User » Thu 05 Nov, 2009 08:45

I think I figured out what happened. The TA was so high it didn't read/test (turn green).

I added granular chlorine first to try and get the chlorine up

Then I added Soda Ash to get the PH up (it was low)

Then added ALK booster thinking the TA was low.

I think the stuff floating on the water is scaling. The PH seems to be locked. These suggest that the ALK was actually too high which can lock PH.

does this seem right?

I still need to clean the filter first before balancing the pool. but when I do balance I guess I need to lower the TA fist before raising the PH.
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