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How do I turn my green pool blue?

renovations1One of the most frequent and annoying situations for any pool owner is an ugly green pool. Nobody wants to jump into green water. Luckily, the solution to the “green pool” problem is not that hard to solve and with proper maintenance and pool attention, you will be enjoying a crystal clear algea-free pool once again. Simply follow the steps outlined below and eliminate the green and bring in the blue!

  • 1. Shock the pool with chlorine every day until all the green is gone (possibly 3 to 4 days).
  • 2. Run the filter 24 hours a day and backwash every day until the green and then cloudiness is gone (usually up to 7 days, sometimes as long as 2 weeks depending on the filter).
  • 3. Vacuum when you feel like it.
  • 4. Adjust pH and alkalinity when algae are gone and chlorine levels have fallen to a safe range for swimming.

If a pool is green, or has green (or possibly yellow or brown) spots on the liner or concrete, you have LIVE ALGAE. Most water testing cannot detect algae, so although your water tests may come out OK, if you have green, you have LIVE ALGAE. It usually feels slimy to the touch. Although vacuuming seems to clear it up easily, it grows back rapidly.

Many things cause green pool water, even if you’ve maintained perfect water conditions. Rain can bring in spores, algae and dirt beyond what the current chlorine level can handle. Algae thrive in warmer water – so if we’re having an unusually warm summer, algae will grow more quickly, and regular chlorine levels should be maintained a little higher than normal.

The only thing that kills algae is CHLORINE (or your sanitizing product, or one of the copper-based algaecides on the market). You need to raise the level of your chlorine – shock the pool – and maintain that high level until all the algae is dead. This may take 3 to 4 days. RUN THE FILTER 24 HOURS A DAY. You must maintain that high level of chlorine. If the chlorine level is allowed to fall, the algae will begin to reproduce and proliferate, and it will take even longer to kill. When the algae is dead, you will probably wind up with milky-white cloudy water. The dead algae floating around cause the cloudiness. IT IS YOUR FILTER’S JOB TO CLEAR THE DEBRIS floating in the water. Continue to run the filter 24 hours a day, backwash every day, until the pool is clear. Clarifiers are available to speed up this process, however, they can create a gummy residue in some filters so it is only recommended after your filter has been given an opportunity to clear the water on its own.

Vacuuming does not kill algae. It may seem to get rid of the green temporarily, but the actual spores on your liner are clear, and live algae will simply circulate – filters don’t kill anything.

It does expose more of the algae to the chlorinated water, and may prevent some cloudiness by capturing particles a little more quickly. Be sure to keep your chlorine level high, and backwash when you’re done.

Most algaecides are preventatives, with the exception of some copper-based algaecides, and do not kill live algae. Some copper-based algaecides have been proven to kill algae, but they work best when algae problems are not extensive, and their best function is as a preventative. Continued use can build up copper levels in the water. Read all product labels before use.


Some large DE filters do not need to be backwashed.

If your sand filter does not clear up the pool within two weeks after running continuously and being backwashed frequently, perhaps the sand needs to be changed. BE SURE TO USE FILTER SAND, not play sand – there is a difference.