Why Do I Still Have A Green Pool?

by Deb
(West Virgina)

Recently bought a home with an above ground pool measuring 18 x 36. When we first looked at the house the pool was hairy GREEN! The owner "cleared" the pool, at least the water was clear the day we moved in, but that was 3 weeks ago and despite every effort, we still have not been able to swim, because the water went immediately cloudy, then murky, now full blown green again.

At the beginning of the cloudy look, I took sample to local pool store, and was informed it needed alkaline. Had me add 5 lbs of alkaline. Continued to get worse.

Took sample to a different pool store, better reputation..., and was told that alkaline was off the charts. Was told to add PH MINUS, I have and 2nd sample took 26 hours later and alkaline still high, 2nd dose of PH MINUS.

That was 48 hours ago, and our water is STILL GREEN! I added 2 lbs "shock" 24 hours ago. I am at my wits end with this green water! It's almost time to close the pool, and we haven't gotten in yet!

Can you help? Much appreciate any suggestions you can offer.

Just got a reading. Free chlorine 0.1
Total chlorine 0.1
Ph UNR 7.1
hardness 160
Alkalinity 83
Cyanuric acid 25
Copper 0.32
Iron 0.14
Phosphate 0

Please tell me my pool is fixable! Thanks!

Thanks for the readings Deborah

First I'll go through the meanings of the readings.

Chlorine is the sanitizer for the pool. The range is 2 - 4ppm for home pools. It kills the algae and bacteria.

CYA/stabilizer/conditioner is the other half of chlorine. You need this because the sun, heat, splash out eats up the chlorine. The range is 30 - 50ppm.

As the CYA increase through using tabs, Trichlor tabs, the chlorine needs to increase as well. If you allow the CYA to get to 100ppm, you need to run the chlorine at 7 - 8ppm for the chlorine to be effective.

When the CYA gets this high the only way to reduce it is a partial drain and refill. There's no chemical to reduce the CYA. Let's use common sense. If your CYA is at 100ppm, and the range is 30 - 50ppm, then by draining 1/2 of the water and refilling it you'll drop the CYA to 50ppm.

The above is the BIG thing that many pool store employees simply don't know. The hear of a green pool and their cure is to shock it. This is across the board patently false. If the CYA is too high, above 70 - 80ppm, it's rendering the chlorine ineffective. There needs to be a partial drain and refill to get the CYA to 30 - 50ppm. If the CYA is too low, below 30ppm as is yours, the remedy is to add Dichlor chlorine. This is a stabilized form of chlorine. Once you reach the 30 - 35ppm CYA mark, stop with Dichlor and go back to regular liquid chlorine.

pH is the comfort level of the water. A range of 7.2 - 7.8 is best.

Total Alkalinity (TA) measures of much alkaline substances there are in the water. It measures your pool water's ability to resist change in pH. The range is 80 - 100ppm, 120ppm being the top.

Hardness is the makeup of minerals and hardness in the water. Normal range is 150 - 250ppm.

Iron and metals is pretty simple. It's metals in the water. This is mostly for well water. If your readings are 0 and you're on city water then don't worry about it. Are you on well water?

I will assume the readings are correct and your pH and TA and hardness are fine. Absolutely no acid of any kind. If you add acid you're going to drop the pH and/or TA. You don't want this.

Now for clearing up your pool. It's going to take some time and work,
but your pool is fixable.

The pool is 18 x 36, about 15,000 gallons, right? It's 1 2/3 gallons of chlorine per 15,000 gallons to raise the chlorine 10Xs. The first thing you want to do is to add just a bit more CYA into the pool using Dichlor. Use 2 2/3 lbs. of Dichlor and 1/2 gallon of regular liquid chlorine to shock the pool.

This will do two things. First, you'll be shocking the pool and 2nd you'll be increasing the CYA. 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. You'll probably only need to use Dichlor once. This will raise the CYA to 35ppm or so. After that, stop using Dichlor and go to liquid chlorine. Never mix chlorine. Add the Dichlor into the pool, sweep, then add the liquid chlorine.

Remember, it's 1 2/3 gallons of chlorine per 15,000 gallons to raise the chlorine 10Xs. I'd use 2 gallons to raise it to 12 - 13ppm. Any higher and you're wasting money and chemicals.

Here's the summary:

1. Shock with 2 2/3 lbs. of Dichlor and 1/2 gallon of liquid and test the chlorine and CYA after 8 - 10 hours of filtering. Remember to take everything out of the pool, ladders, toys, etc... and sweep very well. Broadcast the Dichlor around the perimeter of the pool and sweep, sweep, sweep the floor and walls.

2. Once the CYA is around 30ppm or so, stop using Dichlor and shock with liquid chlorine. You can get a 5 gallon bucket filled 1/2 with pool water. Pour the chlorine in, stir with a stick, and broadcast it around the perimeter of the pool, and sweep very well. FILTER 24/7 and backwash once per day.

Shocking is a process, not an event. The trick is to get AND keep the chlorine above 10 - 12ppm for a period of time. You'll need to manually dose the pool with chlorine to keep it at 10 - 12ppm. Make the adjustment at night, then retest in the morning. Be sure to have the pump running 24/7 and backwash once per day.

You'll know this is working because the pool will go from green to a white/grey cloudy and the chlorine will begin to hold better. First you may lose most of the chlorine, then 2/3, then 1/2, then 1/3, and so on. Once you only lose 1 - 2ppm of chlorine 8 - 10 hours after the last application you know the algae is dead. Now it's just a matter of filtering and backwashing once per day. Broadcast the chlorine around the perimeter of the pool and brush well. This will loosen up any algae adhering to the walls and bottom.

During the shock process I'd recommend using a PolyQuat 60 algaecide. This is the best and has no metal fillers in them. Other cheaper algaecides can cause the water to foam. With vinyl liners, using a cheaper algaecide can also make the vinyl sticky.

Sticky Pool Algaecide On Vinyl Liner

"Soapy" Water After Using An Algaecide

After you get the water right there's no need for algaecides. An algaecide doesn't kill already existing algae, regardless of what the pool store employee may say. It's an insurance policy against future outbreaks.

Again, remember to keep the chlorine level above 10ppm, FILTER, and backwash once per day. This is what many pool owners fail to do and it's a cause of lots of frustration.

And no acid.

If you would like personal assistance, I do phone consultations for a donation of your choice. It makes things go much faster. If you choose to not go that route, we can correspond by email.

Contact Me


Hope this helps and have a great rest of the Summer.


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Sand Filter Not Clearing Green/Cloudy Water

by Ed Gotwals
(Lansdale Pa USA)

Ever since I put in a sand filter I have been having problems with green and or cloudy water. Are their diagnostics to determine if the filter is working correctly?

I read that channels could be in the sand that would preclude or by pass the filtering effect of the sand. How do I check for this condition? How much sand should there be in the filter?

Thanks for the question Ed

You have green/cloudy water for a reason so I'd like to have your complete chemical readings:

Chlorine, CYA (cyanuric acid/stabilizer), pH, Alkalinity, Calcium Hardness, and Metals (iron and copper) and names of any algaecides you may have used along with clarifiers, phosphate removers, and/or flocs. It makes troubleshooting much easier.

If you've recently installed the sand filter, within a couple of years and it doesn't see heavy use, then channeling probably isn't to blame. Channeling happens mostly with high-use pools and can with either residential or commercial. This is when there's alot of oils introduced into the pool through lotions, make-up, sweat, etc...

This oil gets trapped in the sand and is similar to sandy lard. The water can't go through. Since water will always find the path of least resistance it will go around it, down the sides of the filter, and be returned back into the pool as unfiltered water.

You can simply remove the top of the filter and feel around the sides. If there is channeling you'll feel it. It's like a deep hole. There's an easy way to take care of this but I won't go through it until it's confirmed.

The amount of sand depends on the filter model. Let's take the Tagelus Sand Filter. The TA 40/TA 40D model uses 175 lbs. of sand and a 7¾ free board while the TA 50/TA 50D uses 225 lbs. of sand and a 9¼ free board. Check the side of the filter or your owner's manual for the specs.

Too fine of a grade of sand will clog too quickly. Most manufacturers generally recommend No. 20 grade silica sand.

You can check out these pages:

Swimming Pool Sand Filter Problems

"Working correctly" is a very wide range. There's high, low, and no pressure, sand coming back into the pool, out of the backwash hose, no prime, short filter cycles between cleanings, filtration system improperly sized, etc... Each problem is separate.

Also, sand filters are not my first choice. That goes to cartridge filters. I found through personal experience that sand filters, like DE, can be a real pain.

To post a reply, or if you have a similar question, you can see your post on the Q&A page in the "Sand Filters" category.

Check back to this post for updates or answers.

If you need immediate assistance (within 24 hrs) or for emergency personal assistance, you can make a donation of $35 per hour and I'll answer your questions by phone.

If you've found this site helpful please consider making a donation. Thank you.

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


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