Chlorine or Free Chlorine Green Pools

by Mark

I have a green pool at start up of the season. I shocked, then put in algaecide, and vaced a few times it is not the dark green/black any more but a light-green and ver cloudy. I am trying to figure out if the algae is alive or not.

My total chlorine number is 12 and has been for a while. But my Free Chlorine is low (less then 1). If I keep this situation will that kill the algae? (ie does the total chlorine or the free chlorine kill algae?).

Other chemicals are in the right spot, pH a little high though(7.8)

FYI: I often have a phosphate problem with the pool also (evergreen trees nearby)

Am I ok leting this take it's course and having the filter do it's work (with more scrubbing and Vacing) or do I need to do something to free up that Chlorine?



Thanks for the question Mark

I'd like to have the rest of your chemical readings:

CYA (cyanuric acid/stabilizer), Alkalinity, Calcium Hardness, and Metals (iron and copper).
It makes troubleshooting much easier and the process of clearing up your pool will go much faster.

You can get this done at your local pool store. Without these numbers I'm just guessing at what the problem is. The other readings play a factor into how you will approach clearing up your pool.

The free chlorine (FC) kills the algae. The total chlorine (TC) is the sum of the free chlorine plus the chlorine that's already been used up. That's called combined chlorine.

Remember that algaecide is used for preventative maintenance only. It's not used to kill already existing algae. You can use it to augment the chlorine that's already in the pool, but not to actually kill the algae and clear up the pool.

Concerning the phosphate remover, I'd encourage you to be very careful with that. Only under extreme conditions or circumstances should you need to use a phosphate remover. It can cause more harm than good in the long run.

Here's a post about that. A little long but worth the read. Be sure to read the comments on the 2nd page:

High Phosphates Over 1000 & Cloudy Water

The chlorine is already in the pool but is consuming the algae. The CYA and other readings will show how to handle your situation because each pool is different and has different readings.

Get back to me with the chemical numbers and I'm sure I can help.

Hope this helps and have a great Summer.


Comment By Mark
Date: June 8, 2012

Thanks for the quick reply.

I was puzzled because my reading of the chems were different than the store's (when I did strips and liquid testing). But 2 hours ago I found that my alkalinity was down and the ph was high, so I balanced that out (adding alkalinity and then muriotic acid)

I am going to shock it (since I can see the chlorine levels on my tester now) and re test tomorrow. The pool place did have my cyn low, or at 0, so I added stabilizer too.

Hopefully with the pump on, I can get a clear story tomorrow.


Comment By Robert
Date: June 8, 2012

It can get confusing when you get two different readings. If the pool store isn't using an electrical analysis machine, they're probably using a K-2006 kit. This requires swirling that takes some technique to get a good reading. I taught about 30 lifeguards at the Y on how to use the 2006 kit and even while taking readings each hour, it still took them a couple weeks to get it right. I've been using the K-2006 kit since 1999.

Don't spend extra money on any kind of "conditioner" or "extra special stabilizer". You can use Dichlor chlorine. This is a stabilized form of chlorine. Once you reach the 30 - 40ppm CYA mark, stop with Dichlor and go back to regular liquid chlorine.

If you don't have a tab floater, you can pick one up for about $12. They'll last for years. Never put tabs in the skimmer. Even with the pump off they keep dissolving. When the pump turns back on the system gets a huge blast of acidic water.

Be careful when using Dichlor as it can get out of hand quickly. For every 10ppm of chlorine added with Dichlor, you'll raise the CYA by 9ppm. For every 10ppm of chlorine added with Trichlor tabs you'll raise the CYA by 6ppm.

Here's good read:

Do You Really Need All These Chemicals For A Pool Or Are They Just Trying To Get Your Money?

Let me know how it turns out for you


Comment By Mark
Date: June 10, 2012

With the 2006 tester, how high does the cl read? Does it go up to 5ppm or higher? How do you deal with water that has one measure that out of wack?

For my water, the pool store said:
CL 2ppm (fcl the same)
CH 150
CYA 20ppm
TA 80
Ph; 7.0
Phosphate: 300

They are suggesting 6+lbs of soda ash (I have 35k gallons)

The water is cloudy, like can't see 3 feet cloudy, I just got rid of the green by super chlorineating it for 36 hours.

What do you think?

Comment By Robert
Date: June 10, 2012

Thanks for the follow up

You can use soda ash to increase the pH of the pool. 1.5lbs. per 10,000 gallons to increase pH 0.2. Using 6lbs. of soda ash at one time might overshoot the mark. I'd start with about 4.5 lbs, wait 8 - 10 hours of filtration, then retest. Don't test too soon. Many say test within an hour or so, but chances are you're not going to get a good reading. It needs to go through the entire system and be returned back to the pool.

You just want to bring the pH up to 7.2 - 7.4 and allow aeration to take care of the rest of the increase. Splashing around and water features such as slides and water falls will burn off the CO2 causing the pH to rise naturally. Remember that pH means "potential hydrogen" and the burning off of the carbon dioxide will cause the pH to rise. This will save a little on chemical use, and save a bit of money as well.

The alkalinity is right on the low-normal side, but nothing worry about. if it dips below 80ppm you can make a small adjustment with baking soda and it'll be fine. The hardness is fine as well.

Pool Alkalinity

Total Alkalinity

The CYA is still a little low. As per the other email, shock with Dichlor until you reach 30 - 35ppm, then go back to chlorine. Optimal range is 30 - 50ppm. It's great the water is cloudy because of the dead algae, but don't get too comfortable. You need to test in the evening, then retest in the morning and see how much chlorine you lost. If it's 5ppm or more, you might still have algae. When you only lose about 1 - 2ppm, you're good. This is where many pool owners fall short. If the pool looks cloudy then the algae is gone, but it might not be. The test is to see how much chlorine has been lost over 8 - 10 hours.

If you're using a Taylor K-2006 kit, you can measure very high chlorine, up to 20, 30, or more. If you're using a yellow OTO kit or strips, they normally only go to 5ppm or so. Red color on the OTO indicates high chlorine, but you don't know how high. That's why I've used the K-2006 kit since 1999, it's the most accurate and you know exactly where everything is.

Don't do anything about the phosphates and don't allow the pool store employees to sell you anything for phosphates. Here's good post about that. Be sure to read the comments on the 2nd page:

High Phosphates Over 1000 & Cloudy Water

Hope this helps and let me know how it turns out for you


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Jun 12, 2012
White Powder & Chips In Plaster Pool
by: Mark

Perhaps now I am only connecting to dots, or perhaps I am thinking too much...

First of all I have a plaster pool, cartridge filter, 35k gals. Yesterday, when I was lowering the PH, I put the dry acid in a bucket to mix it up, and I dumped the acid mixture in the spa (which is separate, 600 gals or so) and the water in the spa turned milk-white. I thought that was odd, but with my limited knowledge of chemistry I knew that could happen.

This afternoon, I was vac'ing to waste, (like the 3rd time in 4 days) and I noticed a white powder or small chips, like calcium pellets where the discharge hose was.

To add to this, the pool was re-plastered 2 years ago, but we did not have this problem last year.

Are these connected?

Now my chems are; cl 2; CA 150, CY 25, TA 90, ph 7.3, TDS 600.

The pool store said I needed 43 lbs of "hardness plus" (I only had 10 lbs, and just put it in)

Can I get fix this with baking soda? How to I calculate the amount?

Btw; I have an in-line cl feeder for the tabs.

Jun 12, 2012
Calcium Level
by: Robert

If the calcium level is satisfied and the cloudy issue is the plaster, the filter and backwashing should take care of the cloudiness. If some of it settles to the bottom, you can vacuum to FILTER or WASTE.

They both the their good and bad points. WASTE means it bypasses the filter (no backwashing) and you have much more suction, but the water level drops and you need to keep topping off the pool with clean water which can dilute the chemicals.

You can also turn the pump off for 2 - 3 hours and allow things to settle. Turn the pump back on and immediately vacuum.

With FILTER you need to backwash. You probably lose about 250 gallons of water with each backwash which may not be as much as vacuuming to WASTE. It won't dilute the chemicals as much because you're not using so much water to top the pool off.

As long as you keep the chemicals correct you should be fine. Get the CYA to 30 - 35ppm using Dichlor, then go back to liquid chlorine. All other readings are fine. The pH is around 7.2 so don't mess with that.

The pool store might try to sell you a clarifier or coagulant. This clumps everything together and settles to the bottom where you can can vacuum it up. The problems are it sometimes doesn't work, is expensive, and messes with the chemical balance.

It may take a few days to get the water clear once again, but constant filtering and vacuuming should do the trick.

Good luck and let me know how it turns out for you


Jun 12, 2012
Cloudy Pool Water Because Of Plaster
by: Mark

Assuming this is plaster making the water cloudy, and I bump up the hardness to 200, will the cloudless be pulled out by the filter or should I vac to waste or something else to make it clear?

Jun 12, 2012
Follow Up For Plaster Pool Calcium
by: Robert

Thanks for the follow up Mark

The white powder could be calcium hypochlorite if you're using chlorine granules. The white chips aren't normal and could be the plaster coming up. Normal range for calcium hardness is 150 - 250ppm. If you add 43 lbs. of hardness you would effectively raise the hardness by approx. 100ppm. It's 1.25 lbs. to raise hardness 10ppm per 10,000 gallons. If you wanted to raise the hardness level 100ppm, 43 lbs. would be a start.

Your readings look very good. The CYA is still a bit low at 25ppm but nothing that a little Dichlor won't solve. 1 1/3lbs. of Dichlor will raise the CYA 9ppm per 10,000 gallons. Go for 30 - 35ppm, then allow the chlorine tabs to slowly raise it and keep the pool chlorinated through the week.

You didn't mention if the pool was still green or cloudy. Baking soda is to increase the pH and alkalinity. It won't have an effect on the hardness. You don't need to raise the pH or TA because those readings are fine.

Keep your chlorine tab feeder clean. From my experience they tend to gum up. I had to replace one in a retirement home in Arizona at a cost of around $250 for parts and labor. A tab floater costs about $12 and they can last for years.

It could be the chips are from the plaster, or it could be your plaster needs a slightly higher hardness level. It's hard to tell without actually seeing the chips and confirming they're plaster.

By not keeping the hardness in the range of 150 - 250ppm you can have pitting. This is where the water pulls the plaster out because it's hungry for calcium. It won't hurt to raise the CH to 200 or to 250ppm but I wouldn't go higher than that. It seems to be overkill and cost money.

Let me know how it turns out for you


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