Green pool water

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

Green pool water

Postby Kenric » Tue 10 Jul, 2007 09:55

20,000 gallon pool in Phoenix, AZ. 100% Exposed to sun during the day. It's been 110+ for 2 weeks.

Here are my tests from Leslie's pool.

FC 5+ (Their scale only went to 5) My test strip had it around 10+
TAC 5+ (Again, their scale went to 5) My test strip had it 10
pH 7.6
TA 100
CYA 100
TDS 1000
Phos 100ppb

Some history.

I bought this house in April 2007. Whenever I went to look at the house the filter was running during the day. Not sure if the previous owner ran it 24/7 or not.

Pool was blue and staying blue using tabs for 1 month.

Then it got hot here in Phoenix. When pool would turn a tinge of green I would dump in 2-3 bags of shock powder. First it was weekly.

Then, it got to the point where I needed to dump 2-3 bags of shock every 2-3 days. Chlorine seemed to be going from 10 to 0 in 48 hours.

Went on vacation for 1 week. Came back pool was semi green, could almost see bottom at 10 ft. Dumped 5 bags of shock in but Chlorine went to zero within 24hrs. Dumped another 5 bags in and Cl stayed at 3ppm.

Went on vacation for another week. Dumped 5 bags in before I went on vacation. Came back and pool was a deep green, couldn't see bottom at 3ft. Dumped 10 remaining bags of shock, bought 4 gals of Liquid Chlorine.

Also drained 8 inches of water and refilled, my calcs show that's about 3,000 gallons.

FAC remained high for 2 days. Water test is from day 3 back (yesterday). Pool store suggested a Copper/Algaecide. Put in 8 oz yesterday.

This morning took a water strip test, FAC is at 5, TAC is at 10. Pool water smells like chlorine. Still green and can't see bottom but looking better.

Is their anything else I should do?

Should I drain more. I know that CYA is high.


Postby ncroncrew » Tue 10 Jul, 2007 10:18

Firstly, if you have a 10' diving well (deep end) you need to recalculate the water volume of your pool. Chances are, you are not using enough shock to kill algae off completely or to rebalance the combined to free chlorine level.

Because you are shocking the pool, I am assuming you have a chlorine sanitizing system. How are you maintaining your chlorine level. You need a constant feed of chlorine to your water, not just shock. Maintain your chlorine level at around 3.0 with tablets, either in a float or dropped in your skimmer (preferred method). Start off with 3 then check your chlorine daily to maintain level. Add or subtract a tablet as necessary. Make sure your test kit chemicals are current - not outdated or have been exposed to extreme heat or cold (keep it inside). You should not have to shock more than once a week for maintenance probably 3 to 4 lbs. depending on the shock you use. Also use a good algaecide on a weekly basis as a preventative measure - it's expensive, but cheaper in the long run.

If what you are experiencing now is Mustard Algae, you will notice setiment on the bottom of your pool. It will look like brown slime. You can treat it with Bio-Guard Bannish - after you recalculate your pool volume, your pool store can tell you exactly how much to use. Backwash your filter daily until you see no more evidence of the mustard algae. Vaccuum your pool to waste (on the multi-port valve) on a daily basis until you no longer notice any setiment on the bottom of your pool. Then, weekly maintenance with shock and a good algaecide (I get mine from Sam's) should keep in under control.

Also, if you are in direct sun, in 100+ degree heat, keep your filter running 24-7 until things cool off. Algae likes a nice warm environment.

Hope this helps - unless somebody has a better answer.

Postby ncroncrew » Tue 10 Jul, 2007 10:24

Sorry, I forgot a VERY important step. If your water smells like chlorine, it means that you have a high volume of free chlorine. You will need to shock the pool according to your water volume at a VERY high level. My suggestion is to take a sample to a pool store in your area that uses a computerized system of testing your water. Leslie's is great for every-day maintenance samples, however sometimes misses some critical aspects. Last year I had to shock my pool with 55 lbs of shock because the free chlorine level was so high.

Hope this helps!

Postby Kenric » Tue 10 Jul, 2007 14:04

I ran the pool calcs with an average depth of 7'. It's a kidney shaped pool. Based on the calcs it is in between 18,000 and 23,000 gallons. It's largest dimensions are 33' x 18'. With 14' being average width.

Postby Kenric » Tue 10 Jul, 2007 14:06

I was using tablets to maintain the pool. I've stopped using them since the ones I had contain stablizer. For now, I'm manually adding chlorine in the form of liquid chlorine although I do have a few shock bags left.
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Postby chem geek » Tue 10 Jul, 2007 18:20

With your CYA at 100 ppm it's going to take a LOT of chlorine to kill the algae bloom. A minimum of 25 ppm, but 40 ppm FC will have it killed faster, but be sure and add chlorine slowly over a return with the pump running. You could lower the pH to 7.2 before you add the chlorine since that much chlorine will cause quite a rise in pH and you'll want to maintain the high FC level until 1) the water clears and 2) you measure minimal (< 0.5 ppm) drop in FC overnight and 3) you measure minimal (< 0.5 ppm) Combined Chlorine (CC).

However, at a CYA of 100 you'll have to maintain 11 ppm FC anyway (7.5 ppm FC absolute minimum) so you might consider doing a partial drain/refill to lower the CYA level so you can maintain a lower FC level ongoing, and even for shocking to get rid of this algae. Up to you. Or if you do get rid of the algae at this high CYA level, then if you want to use a lower than 11 ppm FC ongoing, then use a weekly dose of PolyQuat 60 algaecide.
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Re: Green pool water

Postby Backglass » Tue 10 Jul, 2007 21:15

Kenric wrote:Pool water smells like chlorine.

One of the oldest pool urban legends is that the smell of chlorine means you have over chlorinated. It's actually the opposite.

If you smell chlorine, you don't have enough and need to reach shock levels to burn off the CC.

It sounds counter-intuitive, but it's true.

Postby Kenric » Tue 10 Jul, 2007 22:41

Can I safely partially drain the pool? It's an inground concrete pool with a basic white painted finish (not sure what its called). I read that it shouldnt be exposed to direct hot sun.

The only way I can drain it is to connect my Kreepy Krauly to the overflow and run it for a day. Maybe I can begin draining in late afternoon and fill it up overnight.

I drained 8 inches and it didnt lower the CYA at all. I'm guess that I need to drain at least 2 ft to get 1/2 the water out.

Postby Kenric » Wed 11 Jul, 2007 10:57

Drained about 2 ft from my pool, probably about 25% of it. CYA seems a little lower, can't really tell from test strip color. What I can tell is that it took longer for the strip to get to the color and that its slightly lighter than yesterday.

TAC and FC is 10+ consistently. Still green but looking better.

Postby Kenric » Fri 13 Jul, 2007 10:18

Did another partial drain and refill, added more liquid Chlorine. Pool looks bluish now but still cloudy (can see about 5 ft down). CYA is down and FC is way over 10+. All I do now is wait right?

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