HELP! My Saltwater Pool Turned Green

School Summary:

If your saltwater pool turns green, it is important to get it turned around quickly. In this article, we discuss how to handle this situation.

What to do when a salt water swimming pool turns green.

Even the best maintained pool can turn green, through no fault of the pool owner. Perhaps you had a very heavy rain that deluged the pool, or maybe the leaf buds off of the tree ate up all the chlorine. If your saltwater pool turns green, it is important to get it turned around quickly. In this article, we discuss how to handle this situation.

Shock the pool

When your salt pool goes green, your pool develops a very high “chlorine demand”.

Important Concept: Chlorine Demand

The “chlorine demand” of a pool is the amount of chlorine that it will take to burn up all of the organic material in the water and leave a chlorine residual in the pool to burn up any other organic material that might get into the water.

When a pool turns green, it creates a very high chlorine demand.

If you have a 20,000 gallon pool and it turns green, you probably need five lbs of chlorine to turn it blue again. Then you will probably need to hit it with another shock treatment the next day.

If your 20,000 gallon pool turns green and has algae growing on the walls, it will probably require twice that amount (10 lbs) to burn up the algae in the water and on the walls.

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Superchlorinating your pool will requires the following chlorine dosage:

1 lb of shock per 10,000 gallons – clear water but less than 1.0 ppm chlorine
2.5 lbs of shock per 10,000 gallons – green water, no visible algae on walls
5.0 lbs of shock per 10,000 gallons – deep green water, visible algae on walls
Note: If you have a colored surface on your pool, spend a little extra and buy the fast dissolving shock.  The less expensive calcium based shock can leave a white film on your plaster over time.

No salt system is capable of delivering this much chlorine this fast.

The “superchlorinate” function on your salt system simply turns the system up to 100% production, but there is no way by industry definitions that this even comes close to superchlorination.

Brush the plaster thoroughly

If you have green water, there is algae growing on the walls, even if you cannot see it. You need to brush the walls, seats and steps vigorously to expose any algae to the chlorine shock in the water.

Until all the algae is removed, you will not be able to return to depending solely on your salt system for your chlorination.

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Test the water every 12-24 hours and shock as often as needed

Here is the thing: If you let the chlorine level drop to zero, the algae will start to grow again and you will end up right where you started. When it comes to algae, you have to keep your foot on its throat, so to speak, until it is totally gone.

Your pool will have a raised chlorine demand for some time, and you need to keep testing and shocking as needed to meet that chlorine demand.

When your testing shows that your salt system is able to meet the demand and maintain a good residual of 1.0 – 3.0 ppm in your pool, then you can stop this emergency shocking and brushing.

There are several possible causes for a green pool:

Organic Matter – this might be a lot of dirt washing into the pool, or buds falling off of the trees, or algae that grew because the chlorinator failed to keep up.

Cell Failure – your salt cell has a lifespan of approximately 10,000 hours.

Salt System Failure – there could be another component of the system that fails, causing the system to not turn the cell on. This could include flow sensor failure, or a control box malfunction.

Salt System Undersized – you might have a system that works fine 10 months out of the year, but when in the extreme heat of Texas summer, it just cannot keep up. In this case you might have to supplement with chlorine tablets or run the system longer.

Salt System Not Set High Enough – you may just need to turn the output of your cell up to match the demand of the pool.

Pool System Not Running Long Enough – your saltwater chlorine generator cannot generate chlorine if the system is not running. You may need to extend your run time to allow the salt system more time to generate chlorine

If you cannot figure out why your salt system is not keeping up with your pool, you may need to bring in a pool professional, who has experience in dealing with these issues.

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