Help.. Can't Keep Chlorine Level

by Lance

I have above ground pool 10,000 gallons with sand filter. The sand was replaced last year before closing. The temp here has been hot for this time of year its been about 85-90's with lows at night in the 70's. Pool water is a little cloudy but not to bad.

Here are my reading at 9:30am and this was after I did a shock the night before at 7:00 pm. Free chlorine .14 Total chlorine .17 alkalinity 138ppm ph 7.3 and cya 54 ...

Is the cya so high that it's taking out my chlorine??? The pool store told me it was because I had phosphates and was telling me to buy some high dollar remover..

Can you help with this information.

Thanks for the question Lance

Your readings aren't too far off. Just a few small corrections and you should be on your way.

First is the CYA. It's just a bit high at 54ppm. It should be between 30 - 50ppm. The only way to reduce CYA is to do a partial drain and refill. The CYA needs to be 7.5% of your chlorine. As the CYA rises, you need to raise the chlorine level to match it. That's the relationship that needs to be met. If you run your CYA at 54, your chlorine will need to be around 4 - 5ppm. That's too high for a residential pool.

I'd encourage you to drain about 1/3 of the water. This will bring the CYA down by 18ppm to 36, then shock the pool with liquid chlorine.

Next is the alkalinity. 138ppm is a little high, but nothing to worry about. It should be between 80 - 100ppm, 120 being the top. You'll use 0.8 qts. per 10,000 gallons to lower the alkalinity 10ppm.

Check the alkalinity and pH of the fill water first. If it's low, the partial water change will automatically lower it because you're diluting the pool water by introducing low alkalinity water into the pool. If the fill water alkalinity is high, you'll need to use acid to bring the alkalinity down.

Turn off the pump and add the acid in one spot, then very gently sweep the bottom to break up any hot spots of acid. Let it sit for 3 - 4 hours, turn the pump back on and run it for about 8 hours, then retest.

Pool Alkalinity

Total Alkalinity

The pH is fine so don't worry about that. I tell people to run the pH between 7.6 - 7.8, but 7.2 is fine. You raise it by using baking soda, but a 7.2 reading is good. You don't need the added expense of another chemical.

Concerning the phosphates, you need to read these posts. They're a little long but worth the read and time investment:

High Phosphates Over 1000 & Cloudy Water

Don't be concerned with phosphates. The kind the YMCA pool used, before I got there and put a stop to it, was $1 per ounce. A 32oz. bottle was $32 and they were going through 4 - 5 bottles per week. That $6600 per year just in phosphate remover.

To sum it up:

- Test the fill water so you'll know the alkalinity and pH of the water going into the pool

- 1/3 drain and refill to get the CYA to around 35

- Alkalinity to 80 - 100ppm and if the pH is still around 7.2 or so, just leave it

- Shock the pool with liquid chlorine

- No phosphate removers

- If you don't have a chlorine tab floater, I'd suggest getting one. They're about $15 and last for years. Never put tabs in the skimmer.

- Be sure to document everything (times, chemical (s) and amounts, etc...)

Remember to make adjustment (s) in the evening then retest in the morning and make another correction if needed. Keep the filter running through the night. The water needs 1 full turnover before testing and adjusting. This is about 8 - 10 hours. If you need to make 2 corrections, but with different chemicals (example: acid and chlorine), allow 2 - 3 hours between applications. This is where patience comes in handy.

There could be 100 reasons why a pool goes cloudy but many times it's the start of an algae bloom so you'll want to do this quickly.

Cloudy Pool Water

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Hope this helps and have a great Summer.


Comment By Lance
Checking on my samples

Ok here goes again.. I have a 10,000 gal above ground with a sand filter. Had to check on size but got the correct one.. Had a high Cya so I took out some water and put new in. My readings now are PH 7.4 ALK 90 CYA 40 free chlor 4.5 total chlor 1 but I still have a little cloudy water.

I did a super shock thurs got readings up to 11 .. What should I do next???? Also I'm a little confused about how to determine what to keep my chlorine level at.

Comment By Robert
Date: June 2, 2012

Thanks for the update Lance

I know it can get confusing about the free and total chlorine, but hopefully this will clear it up.

Total chlorine (TC) is the sum of free chlorine (FC) (available chlorine that kills algae and bacteria) and combined chlorine (CC) (chlorine that has combined with ammonia. It's already used up and not a disinfectant). Your TC and FC should be the same. When the TC and FC are the same it's good because the CC should be zero. When there's a spread between the TC and FC it usually means there's CC.

Basically, you don't want any CC.

Normally when a pool owner has cloudy water with your readings, it's an early sign of an algae bloom. All the readings are in line, but based on the earlier readings, it could be algae.

Your readings from the last email:
"Free chlorine .14 Total chlorine .17 alkalinity 138ppm ph 7.3 and cya 54 ... Is the cya so high that it's taking out my chlorine???"

Shocking is a process, not an event. You need to keep the level up 10 - 12ppm for a period of time. You can shoot for 15ppm, but no higher. After that it's overkill and you're just wasting money and chemicals. Take the chlorine reading, shock in the evening, filter 24/7, then retest in the morning and shock again. Retest in the evening and shock again. Document everything so you can see a pattern.

Once you keep doing this you'll notice the chlorine level is holding more and more. You might shock then retest in the morning to see you lost 1/2 of the chlorine. Then you may only lose a 1/3, then a 1/4, and so on. By this time you'll know you're winning the battle. No algae can handle that.

But it does take time, persistence, and patience. There's no easy or simple way to do this, and there's no magic in a bottle, regardless of what any pool store employee might tell you. By getting and keeping the chlorine level up above 10ppm, you'll win. I know this personally because I've done it hundreds of times and vacuumed for thousands of hours.

Don't mess with the pH, alkalinity, or CYA, they're perfect.

You want to keep the chlorine level for a residential pool between 1.5 - 3.5ppm. For a heavily used pool or if you're going to have a pool party, you can keep it at 3.5ppm, even 4.5ppm is alright. I keep the Y salt pool between 3.5 - 4.5ppm and everything is fine.

1 gallon of chlorine per 10,000 gallons to bring the chlorine level to 10ppm. I'd use 1.5 gallons to be safe. It's better to go a little over than under. Be sure to brush the entire pool very well to break up any hot spots of chlorine.

I always liked to keep the pools on my route at 2.5ppm. It's not too high but it gives a slight buffer so won't bottom out.

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


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CYA Added Through Skimmer

by Michelle

I have a question. I'm taking care of my neighbor's pool since she loves the way my pool is. I have clear water, but not hers... So today I've added the CYA through the skimmer and it directly returned into the pool and I was left with the white CYA granules all over the bottle of the pool floor. I've tried to dissolve it, but it's almost 10 PM and well the sun is gone. Is it possible that my neighbor's filter sand doesn't filter like it should. She told she changed her sand and the broken lateral this year.

Thanks for the question Michelle

Granular CYA should be added through the skimmer, as you described. It gets caught in the filter and is evenly dispersed into the pool through the returns. It shouldn't be going back into the pool in its granular form. It could be the filter has a broken lateral or stand pipe. 99% of the time this is why sand and/or debris goes back into the pool. Granular CYA does take a few days to completely dissolve. If it immediately went back into the pool I'd suspect a broken lateral/standpipe as was mentioned. I'd also check the Multiport Valve and spider gasket and be sure they're intact.

If you feel your situation is more complex than this, I do phone consultations. It makes things go much faster and many people have found it extremely beneficial, saving them time and money in the long run. All your questions will be answered. I have nothing to sell you so you know I'm not bias.

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Hope this helps and have a great Summer.


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