If Your Pool Is Green and Cloudy Even After Shocking

Updated on May 10, 2017
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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. 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.

Cartridge pool filter
Cartridge pool filter | Source

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

Filtration issues could be the problem. Shocking the pool alone will not clear it up. Pool water needs to be filtered, and will not clear up very quickly if you have a filter that doesn't work properly. It doesn't matter how much shock you put in the pool if you have a bad 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.
  • A cartridge filter must have a good cartridge and be cleaned DAILY if your pool is cloudy, until the pool is clear. A cartridge can only handle so much.
  • If you have a DE filter and the pool is cloudy, then without question, the filter is either not being backwashed and the DE is not fresh, or it is defective and not working properly. A pool with a good working DE filter will not normally be cloudy if the pump is being run on a long enough cycle. 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 repair, and your pool will remain cloudy until the repair is made.

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


2. Why Is My Pool 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 why your pool may still be green even after you've exhausted yourself adding tons of chemicals.

  • Stabilizer. Levels of stabilizer or cyanuric acid can become elevated over time rendering the chlorine molecules useless. High stabilizer can cause the chlorine (Cl2) molecules to "lock up" making the chlorine an ineffective sanitizer. High stabilizer is normally found in pools that use chlorine tablets. The tablets, usually "tri-chlor" tablets, have stabilizer in them, and after you use them for a time stabilizer levels can become out of control. Although you get a very high chlorine reading on your test kit, the chlorine is simply not able to work.
  • Phosphates. High phosphate levels can surely cause algae problems. Phosphorus levels can increase because of leaves or organic debris in the pool. Also, if you spray fertilizer near or around your pool, phosphorus from this can drift into the pool water raising the level. Because algae feed on phosphates, algae blooms due to phosphorus can become overwhelming in the summer months when the water temperature exceeds 78-82o F. This condition is easily treatable with phosphate remover.


In my experience, a bad filter is usually the most common cause of cloudy water. Green pool water is caused by a bad chemical balance, usually something other than just low chlorine. Please look through some of my other articles for more solutions for your pool and check back often as I am always updating my articles.

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

"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 or small is the pool? How "green" is it? If your pool is a normal residential-sized pool (13,000 - 25,000 gallons; the pool pictured at the top of the article is around 18,000 gallons), then let's consider these options: liquid chlorine, or granular shock. The choice depends on what type of filter it has.

  • If it is a sand or cartridge filter I would use liquid chlorine, about 10 gallons, or four of the yellow "Jerry-jugs," The reason for this 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). 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.

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.

Shocking alone does not clear up a green or cloudy pool. This is what a filter is for. If the pool is filtered properly, you won't need a clarifier solution. In some cases a flocking agent can be used, 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.

Test the water after 24 hours and start adjusting pH and alkalinity levels. The chlorine will still be elevated, but over a few days it should stabilize. Sodium thiosulfate can be used to lower the chlorine level, but I do not recommend this. If too much is added it will become a game of how much chlorine to add to raise the level.

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 Timer?

This question applies to normal pools, not just green pools. A pool pump must run long enough to reach a certain "turnover rate." Turnover rate is the time it takes for the circulation system to move the number of gallons equal to the volume of water in the pool through the filter equipment.

This is also a seasonal thing. During the hot summer months, an average-size residential pool should filter for a minimum of eight hours. But during the cold season, since algae have a difficult time growing in cold water, the filter time can be cut in half. You can also cut the filtering time in half when the pool gets no use, but the pool water does need to be filtered whether it is being used or not.

Questions & Answers

    © 2012 Rob Hampton


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    • furniturez profile image

      furniturez 5 years ago from Washington

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