My Pool Water Is Green

by Carl

I have a 28 ft round pool 20,000 gallons. I drined the pool, put in new water, new sand in the filter, water was great for about 3 weeks. Checking chemical level every day.

The levels were fine but it started to turn green slowly, all levels were correct, now it is dark green.

Chlorine, pH, alk, all correct used shock and algae guard as well. Every Sunday, backwash filter once a day the pool is in the sun 5 hrs a day shade the rest of the day.

I just put in 4 gallons of liquid cholorine yesterday but it's still green before I drained it and refilled it.

I went to my local pool place and spent $300.00 in chemicals with no help so I started over with new sand and water. I went back to local pool place did what they suggested.

I'm back to green water as discribed above. Will I need to wait a couple of days for the cholorine to work? The levels are high 10+ on chlorine 8+ on pH. Please help me if you can. I think my local pool place is just trying to sell me chemicals that are not working.

Thanks for the question Carl

First, I'd like to have your complete chemical readings:

Chlorine, CYA (cyanuric acid/stabilizer), pH, 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.

I'd encourage you to get a Taylor FAS-DPD K-2006 pool test kit.

Pool Water Testing

Water Testing Kit

Unfortunately I'm at a loss with chlorine and pH as "correct".

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


Comment By Carl
Date: August 8, 2011

Here's what you need
CYA 30-50 Local pool place closer to 50
PH 8.6
ALINKALINITY 214 was 257 rained last night.
20,000 Gallons of water.
SAND FILTER New sand this year.

I was reading I migh have to do drain/fill if the CYA is too high. What precentage of water do you suggest?

Comment By Robert
Date: August 9, 2011

Thanks for the reading Carl

You can still have an algae bloom even though, when the chlorine is tested, it's above 5.0ppm. This is normally because of inconsistent chlorination.

The CYA is fine. Normal range is 30 - 50ppm. It's the pH and alkalinity that you need to work on. Anything over 8.0ppm pH and the chlorine will only be 25% effective. And the alkalinity is way over. The range is 80 - 100ppm, 120 being the top. Calcium hardness is not so important with a vinyl pool so next year you'll want to keep it around 100 ppm or so. Nothing higher is needed.

You need to get the alkalinity (TA/total alkalinity) down to an effective level. Your TA is 257 which means it needs to come down to 100, or a 157ppm drop. You're going to need alot of acid so just be prepared. To reduce TA in a 20000 gallon pool 100ppm you'll use 4 gallons of acid. I personally would start with 3 and see where that leads. You don't want to overshoot.

Pool Alkalinity

Total Alkalinity

Start this process in the early evening.

Turn the pump off. Get a 5 gallon bucket filled with pool water and then add the acid. Stir with a PVC pipe or stick put it in one area (deepest part if you can) of the pool. Very gently sweep the sides and bottom to break up any hot spots. You don't want to mix the acid too much. Allow this to sit for 3 - 4 hours then turn the pump back on.

Now to shock the pool after you turn the pump back on

Don't shock with regular chlorine granules. It has a pH of 12. If you shock with granules the pool pH will go through the roof and you'll be adding hardness to the pool. You want to use liquid chlorine.

For 20,000 gallons, 2 gallons with bring the chlorine level up to 10ppm. Use 2 1/2. It's better to go a little over than under.

Again, get your 5 gallon bucket filled 1/2 with water and then slowly add the chlorine and stir. Broadcast around the perimeter of the pool. Sweep the sides and bottom to break up any hot spots of chlorine.

You'll want to get the chlorine level up to 12 - 15ppm. Shock in the evening, then retest the chlorine, pH, and TA in the morning. You'll see how much chlorine has been used through the night. You can make another small TA adjustment if needed. The TA charts can be found in the alkalinity links below.

During this process you can use a PolyQuat 60 algaecide as an added backup against any algae blooms that might occur.

The trick in clearing up your pool is to get the pH and TA in line and keeping the chlorine level above 12ppm for a period of time. That's why you shock in the evening, retest in the morning, then shock again.

Be sure to back wash every day. You're going to go through some water because of back washing so keep the water level up 1/3 - 1/2 up from the skimmer.

Remember to test morning and evening and keep the chlorine level at 12ppm or above as best you can. You may need to do this for a few days.

When the pool turns a white/gray color and you only lose 1 - 2ppm of chlorine through the night you'll know the algae is dead. If the chlorine loss is more you probably still have some residual algae.

Here are some chlorine links to help:

Swimming Pool Chlorine

Pool Shock

Pool Chlorine

Chlorine Tablets

Pool Chlorine Tablets

Hope this helps and have a great rest of the Summer. Let me know how this turns out for you.


Comment By Carl

Did as you suggested cholrine is 10+
pH 7.2
alka 145
cya 40

Today is the second day pool water is still green, it's lighter, but still green. Will a clarifier help? And I did put in a algae guard at time of shock.

Any suggestions.

Comment By Robert

Thanks for the follow up Carl

The readings look good. The alkalinity is still a bit high, but much better than it was. No clarifiers. They don't address the problem of why the pool is cloudy, but and you know why it's cloudy. It's the algae, so you're addressing it.

Only use a PolyQuat 60 algaecide during this process, not a 30 based or copper algaecide. Pool stores and manufacturers push copper based algaecides because it's cheap to make and the profit margin is higher.

I've been getting many questions on the process of how to clear up a green pool so I recently wrote this page:

Green Pools

It's basically this: Test in the evening, shock the pool, retest in the morning to see where the chlorine is, then shock again. Keep filtering 24/7 and clean/back wash the filter once per day.

Everything you need you can find in these two posts. Again, keep the chlorine level up 12ppm or over for a period of time. Shock with liquid chlorine because granular chlorine has a pH of 12 and you'll be behind if the pH rises again.

Hope this helps and let me know how you're doing with the pool.


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Swimming Pool Red Slime...Red Algae

by Sharon

I was swimming at a friend's pool when I noticed a pinkish substance on the bottom of the pool. My friend said it was probably red slime which can sometimes occur in a pool. He vacuumed the the whole pool then everyone (five other people) went back in to swim.

Also his daughter was having a pool party the same day for eight lifeguards from the local lake where she is head lifeguard. I was curious about the health risks of red slime so I researched it on the internet.

The only information I found was your article about how to get rid of red slime and how no one was to swim in the pool until the problem was cleared up. Do you know what red slime health risks are or do you know who to contact to find out?

Thanks for the question Sharon

From my experience red algae/slime can be one the hardest kinds of bacteria to kill. Yes, it's a bacteria, not really an algae like green or blue-green kinds of swimming pool algae.

Because red slime is really a bacteria, you need to approach it a little differently. You can go to this link to learn about red algae:

Red Algae

There's a product that I've never used but I've heard of some people that have had success with it. This product is called "Yellow Out" by Coral Seas. You might find them at this link:

You'll need to add yellow out and then the chlorine at the points where the red algae is the worst. Bring the chlorine level to a shock level of 10 - 12ppm up from your normal chlorine level. You'll need enough chlorine for 3 consecutive shocks.

Swimming Pool Shock

There is a man named Fred at Coral Seas that can help you with most of your red algae problems if you need more assistance or questions. The 800 number is available on the package label and in the website. I'm not aware of any long term health risks associated with swimming in a red algae, but I'm not a biologist. For more in-depth answers you might want to contact the Center For Disease Control.

Hope this helps and have a wonderful rest of the Summer


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