Why Is My Pool Green and Cloudy Even After Shocking?

Updated on July 7, 2018
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Rob is a licensed pool service industry professional with over 20 years of experience.

Judging from the questions pool owners ask on the internet, they are having a hard time with water clarity even when they think all the chemicals are balanced. We will discuss in this article why chlorine, pH, and alkalinity are only the beginning in maintaining clear pool water, and then we will troubleshoot the problem.

Basic Chemical Requirements for Clear Pool Water

Just to summarize, these are the basic chemical requirements for a pool that stays clear. But there is a little more to it than the basics, as you can see in Question 2 below.

  • Free chlorine. Unless the water has a sufficient level of free chlorine, algae will grow and make your pool green and cloudy.
  • Correct pH. For normal use, your pool’s pH should be between 7.4 and 7.6: for shocking, it should be between 7.2 and 7.6. Shocking a pool with too high pH will cause cloudiness.
  • Correct alkalinity. The right range of alkalinity (dissolved salts that keep pH stable) makes pH and chlorine levels easier to maintain.

So What Do I Do Now With My Green and Cloudy Pool?

Read each of the five questions below: at least one should relate to the problem you are having. Most of these questions are based on real keyword searches that have found some of my articles.

Just to summarize my experience: a bad filter is the most common cause of cloudy pool water. Green pool water is caused by a bad chemical balance, usually something other than just low chlorine.

1. I Shocked My Pool, So Why Is It Still Cloudy?

If your pH is not too high, filtration issues are likely the cause of your cloudy pool. The issue may depend on the type of filter.

  • If you have a sand filter, it could take a week or more for the pool to completely clear. That's even if it's a good working sand filter.
  • If you have a cartridge filter, it needs to have a good cartridge. A cartridge can only handle so much. If your pool is cloudy, the cartridge needs to be cleaned DAILY until the pool is clear.
  • If you have a diatomaceous earth (DE) filter and the pool is cloudy, then
  • either the pump is not being run on a long enough cycle,
  • the DE is not fresh because it’s not being backwashed,
  • or the filter is defective and not working properly. Do you have torn filter grids? A broken manifold? Does DE powder shoot back into the pool when you add it? If so, the filter needs to be taken apart and cleaned or repaired, and your pool will remain cloudy until the repair is made.

So remember, a cloudy pool can be caused by a bad filter.

If the pool is being filtered properly, you won't need a clarifier solution. In some cases you can use a flocking agent, a product called "drop out" or "drop and vac," that will bind small particles together and sink all of the algae to the bottom of the pool where it can be vacuumed up as waste.


2. I Shocked My Pool, So Why Is It Still Green?

This is one of the most often searched questions. High levels of the wrong chemicals may be the issue. Let's take a look at reasons why your pool may still be green even after you've exhausted yourself adding tons of chemicals.

  • Stabilizer. Over time, if you use tablets (like Tri-Chlor) to supply chlorine, levels of the stabilizer from the tablets (cyanuric acid) can become elevated over time and “lock up” the free chlorine molecules (Cl2). Even if you get a very high chlorine reading on your test kit, the chlorine is simply not able to work at killing algae because it’s not in the right chemical form. This article shows you how to lower stabilizer levels.
  • Phosphates. High phosphate levels can definitely cause algae problems. Phosphorus, or phosphate, can enter the pool by leaching out of leaves or organic debris in the pool, or drifting there from fertilizer sprayed near or around your pool. Because algae feed on phosphates, algae blooms due to phosphorus can become overwhelming in the summer months when the water temperature exceeds 78-82° F. This condition is easily treatable with a phosphate-removing product like this one.

3. How Much Shock Should I Add to the Pool? Did I Add Enough?

"Shocking" a pool that has turned green is better known in the industry as "super-chlorination."

When shocking the pool, consider a few factors. How big is the pool? How "green" is it? If your pool is a normal residential-sized pool of 13,000-25,000 gallons (the pool pictured at the top of the article is around 18,000 gallons), then your options are liquid chlorine or granular shock. The choice depends on what type of filter it has.

  • If it is a sand or cartridge filter I will use liquid chlorine, about 10 gallons, or four of the yellow "Jerry-jugs." The reason I use liquid chlorine is that granular chlorine will leave a residue that is harder to filter out.
  • If the pool has a DE filter, then I will use granular chlorine (about 5 pounds). This article shows how I shock a pool with a DE filter. Remember to test the water before adding shock. The pH should ideally be low when shocking the pool (around 7.2) because shocking the pool will raise the pH level.

Remember that shocking alone does not clear up a green or cloudy pool; that is what the filter is for. It doesn't matter how much shock you put in the pool if you have a bad filter.

4. Will the Pool Turn Green If I Don't Add Chlorine?

Believe it or not, I have seen this keyword search pop up more than once. There is a short answer: YES, IT WILL turn green if you don't add chlorine. Pool water must have a sanitizer or something that will kill bacteria and algae. Algaecide alone without chlorine will not prevent the pool from turning green.

5. How Long Should I Run the Pool Pump? Am I Filtering My Pool Enough?

Always run the pump when shocking the pool and allow it to circulate for 24 hours. The water should then be a blue or cloudy blue color.

Test the water 24 hours after shocking and start adjusting pH and alkalinity levels. The chlorine will still be elevated, but over a few days it should stabilize. To lower the chlorine level, you could add sodium thiosulfate, but I do not recommend this, because adding too much can cause the chlorine level to seesaw back and forth.

After the shocking process is complete, and you are back to normal operation, you need to set your timer so the pool is filtered for a long enough time each day to deal with any algae or debris. How long to run the pump depends on the turnover rate: the time it takes for the circulation system to move the entire volume of water in the pool (the number of gallons) through the filter equipment.

During the hot summer months, an average-size residential pool that is in use should be filtered for a minimum of eight hours. During the cold season (since algae grow slowly in cold water), or when no one is using the pool, the filter time can be cut in half. But the pool water does need to be filtered whether it is being used or not.

Questions & Answers

  • How do you clean a sand filter in a pool?

    A sand filter is cleaned by reversing the flow of water through the filter by using a diverter valve to push the gathered debris out through a waste line or hose (back-washing). If this question refers to actually changing the sand, this is done by removing the filter lid and vacuuming out the old sand with a Shop-Vac then replacing it with pool grade sand.

  • The pool has algae on the walls but is clear. Why did it turn a cloudy white color right after I shocked it with two packets of shock?

    In the pool industry, we refer to this as "smoking the pool". This happens when a granular shock is added while the pH is high and alkalinity is unbalanced. This can also be resolved quickly by balancing the pH and alkalinity. Before adding granular shock to the pool, be sure the pH range is between 7.2 and 7.4. The alkalinity should be 80 to 120 ppm, with 90 to 100 being ideal.

  • How long after increasing the alkalinity do I wait to shock the pool?

    Before shocking the pool, be sure the pH is between 7.2 and 7.6. Alkalinity should be at least 80 ppm and no higher than 120 ppm. (90 - 100 ppm is ideal) If an increase is needed, add the sodium bicarbonate or "alkalinity up", then allow the water to circulate for at least one hour and then re-test the alkalinity level. Once these levels are balanced, the pool can be shocked.

  • Do I need to add calcium to my above ground pool?

    Calcium is essential to maintain in ANY pool. Water needs calcium. If the calcium chloride level falls below 200 ppm and is not added, the water will still get the calcium that it needs by pulling it from the surface, pool liner, plumbing anywhere that calcium can be extracted from. It's important to maintain a proper calcium hardness level to prevent any scaling, staining or damage to the pool and/or pool equipment. Ideally, the calcium level should be maintained between 200-400 ppm.

© 2012 Rob Hampton


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    • furniturez profile image


      5 years ago from Washington

      No wonder my neighbors pool is green! Lots of insight thanks so much.


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