Pool Water Light Green Color

by Don Ahlbrandt
(Tuckerton, NJ)

Pool 4x15 above grnd 6-7000 gals?

Free chlorine 0 low?

pH 7.4 ok?

Alkaline 40 low

Stabilizer 0 low?

With shock added twice


Been run several hrs. and been backwashed.

Whats my course of action?



Thanks for the information Don

First, if you don't already have one, I'd suggest a Taylor FAS-DPD K-2006 pool test kit.

Water Testing Kit

Pool Water Testing

It would really be time ineffective for me to write exactly everything the questions says. There are several steps involved with how to raise and keep the chlorine level up, how to clear up a green pool, raise the alkalinity, etc...

I've written about all these things, so the best course of action is for me to give you the steps, then give you the links to those steps.

Swimming Pool Chemistry

This way you can get all the details. You can look them over and go through them one at a time.

You can also go through the Q&A page. There are hundreds of questions answered, many of them in the "Algae/Green Pool Water" section.

Swimming Pool Questions and Answers..Pool Forums

First is the right pool kit, as stated above.

The pH level is fine, so don't worry about that.

The alkalinity is a bit low, but we need to be concerned with the algae problem.

Get some Dichlor shock. This does two things; it raises the chlorine level and cyanuric acid (CYA/Stabilizer).

Swimming Pool Chlorine

Pool Shock

The FAS-DPD kit has the test for that. You want to watch that the CYA doesn't go too high or you'll need to drain 1/3 - 1/2 of the pool and refill.

You can also test for chlorine demand.

The charts you need for a good shock can be found on the chlorine pages.

Chlorine Demand

This will start you on your way to clearing up the algae problem.

Swimming Pool Algae

Green Pool Water

Keep filtering 24/7 until the pool has cleared up. When the chlorine starts to kill the algae, the water might turn a grayish/white. This is normal. You'll need to manually dose the pool with chlorine. Test the pool water daily and keep the chlorine level above 7ppm.

The algae will be eating up the chlorine, so your chlorine levels will keep going down until the algae is gone.

Backwash every day until the water clears. Be sure to keep the water level up. This is 1/3 - 1/2 up from the bottom of the skimmer. If the water level gets too low the system will draw in air and decrease the filtration.

Swimming Pool Sand Filters

Remember to take daily chemical readings and keep a log of what they are and the times they're taken.

Once that's taken care of, it will be time to adjust the alkalinity.

Pool Alkalinity

To raise the total alkalinity you'll need to have the pump motor off.

Hope this helps and good luck with your pool


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Why Can't I Clear My Green/Blue Pool Water?

Our in ground 22,000 gunite pool has been impossible to get completely clear. It started very green a month ago and after shocking it several times and putting clarifier in 3 times it is still not completely clear.

I can see the bottom and it is in between blue and green with dust on the bottom. I have a cartridge filter and a Ray Vac pool cleaner. I have cleaned the filter several times.

The chemicals are:

Chlorine 10ppm

pH 7.4

Alkalinity 80

Hardness normal range

Cyanuric acid 100


Thanks for your question

First you always need to be sure you're hitting the shock point. Whenever I shock a pool I always go for a little extra, maybe 12 - 15ppm. It's better to go a little higher than lower.

All of your chemical ranges seem to be fine. It's the cyanuric acid (CYA) I'd like to touch on.

It seems like your CYA is a bit high for your chlorine level. Your chlorine run 7.5% of your CYA and the normal CYA range is 30 - 50ppm.

With a level of 100ppm, your chlorine needs to be about 13ppm to be effective. The only way to reduce the CYA is to drain 1/3 - 1/2 of the water, refill, and balance the chemicals.

I would suggest this right to reduce the CYA to 30ppm then manually dose your pool daily with chlorine to keep the level between 13 - 15ppm. This will be more in line with the CYA reading you have now.

Clean the cartridges every day. You can also get another set and swap them out with the old ones. The next day clean them and swap them out. By doing this you'll reduce any down time. Watch the clarifiers because adding too much can actually backfire on you and cause more problems in a short period of time.

Your pH and alkalinity are fine. Be sure to use liquid chlorine as granular will increase the pH level and you don't want that. Chlorine works better at pH levels around 7.0. Really, the only way to clear up an algae problem is to shock, filter, backwash, brush, vacuum, test, and make chemical adjustments.

One of the main things people do is to allow their chlorine to get below 10ppm while clearing their pools. Again, remember to manually dose your pool and keep the chlorine level up above 10ppm while you're going through this.

Here are some good questions that I've answered about clearing up green pools:

How To Clear Up A Green Pool In Woburn


There are links to the pages about chlorine, shock levels, and how to clear green pools.

And lots of information on the Q&A page about green pools and algae:

Swimming Pool Questions and Answers

Thanks again for giving me your chemical readings. It makes my job much easier when I know what they are.

Good luck with your pool.


Comments for Why Can't I Clear My Green/Blue Pool Water?

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Jan 22, 2015
Green Pool Solution
by: Angelina Mike

Because It is not possible at home, even after a long struggle you have to give up and choose the swimming pool service company once to fix this issue.

Thanks for the comment but anything is possible when you have the right information. The problem with most things in life comes down to lack of proper information from those who know. We will listen to anyone about anything if they're good looking or know how to put their words together in a nice neat little package. Just because someone is wearing a suit, has a microphone and is standing on a stage does not mean he's right.

Listen and get information from the right people who have proven themselves. Those that walk the talk and have evidence that what they say is true.


Sep 05, 2015
Clearing a Green Pool
by: Anonymous

Clearing a pool is easy. Bring chlorine up to 20 ppm free chlorine and use a brush on a pole to scrape all the side walls and the bottom of the pool. This brings all the algae and other crud up out of the nooks and crannies in the rough gunnite bottom of a pool, thus allowing the chlorine to attack it. If you do not brush the pool surfaces the chlorine cannot fully access it and cannot kill it and your problem will return. You need to keep the 20 ppm free chlorine level for several days adding chlorine as necessary because it will be depleted as it kills the algae and other contaminants. Continue to brush the walls and bottom twice a day to prevent algae reattaching. Your first clue that there is algae and crud is when you brush and a bloom of colored material forms in the water right where you brushed.

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