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Why Your Pool Is Still Green After Shocking (7 Reasons)

It’s a beautiful summer day. You feel like going for a swim. You go to your backyard only to be greeted with a pool that looks like it’s been on a week-long bender.

That’s right. You’ve got a green pool

So you do some research and are told to shock the pool to clear it up. But the pool is still green after shock is applied.

What gives?! 

Pool Still Green After Shock?

So you thought your green pool would be easily fixed with some shock? Here are some reasons why that didn’t work.

1. It Wasn’t Caused By Algae

Did you know that algae growth isn’t the only reason your swimming pool water can turn a murky shade of green?

The first is water with high copper content. This primarily happens when first opening your pool. You fill it up, shock the pool, and then it goes green.

It all depends on how much copper the water source contains. Well water is notorious for having high copper levels, so your pool will be more susceptible to turning green if this is where you get your water from.

Copper is a metal prone to oxidation (just look at the The Statue of Liberty). When shock chlorine oxidizes the copper, it turns green and that’s what you’re seeing in the pool. To get rid of it you’ll need to raise the pool’s calcium hardness by adding calcium chloride.

The other culprit can be high levels of pollen. Tree pollen, grass pollen, weed and ragweed pollen can easily get into the pool water when it’s pollen season.

Pollen floats around in the water, so it’s easy enough to remove by skimming, filtering, and brushing your pool clean. In some cases it can be stubborn, so you may have to bust out a pool vacuum and perform this cleaning ritual a few times to remove every speck.

Your best line of defense against pollen is staying on top of your pool maintenance. Running your filtration system is key, as a stagnant pool is one that will develop problems.

Ensure your pump and filters are always at optimal performance, skim the pool multiple times a day, and maintain your backyard surroundings to reduce pollen levels.

2. You Didn’t Brush Thoroughly

Like a toothbrush is to healthy teeth, a pool brush is to a healthy pool.

From algae, to pollen and other organic debris, your pool walls might still have stuff stuck to them that’s causing the green water.

This will be especially present in the pool’s dead spots. These are areas where the circulation system doesn’t quite reach, allowing for pollutants to build up.

When it comes to pool brushes, make sure you have the correct one for your specific pool finish. Steel bristle brushes are ideal for hard surfaces like plaster or concrete, while softer bristles work well for finishes like tile.

The last thing you want to do is scratch your finish or have an inadequate cleaning tool!

3. You Didn’t Vacuum Thoroughly

While you don’t want to just stick a pool vacuum in a toxic swimming pool and hope for the best, it does have its place when trying to restore a pool.

Vacuuming is one of the last parts of the cleaning regimen, after skimming, brushing and running the filter.

It can be a labor intensive job and time consuming, leading to many people cutting corners, which means insufficient removal of pollutants. 

4. You Didn’t Shock Properly

Did you shock the pool with the proper amount of shock? 

It’s pretty hard to screw up shocking a pool, but if your calculations are wrong, you may have under-shocked the pool.

Keep in mind that green pools usually need a few rounds of shocking to get them back under control. Shock dosages are usually 1 bag per 10,000 gallons of pool water.

It’s recommended to use granular calcium hypochlorite shock, or a large dose of sodium hypochlorite (liquid chlorine) if that’s your chlorine of choice.

5. Your Filter System Isn’t Doing Enough

A stagnant pool is a ticking time bomb. 

Proper water circulation and filtration will keep your pool sparkling clean. This is because these two processes constantly mix up the sanitization chemicals, deliver them to every inch of the pool, and filter out impurities quickly.

If you aren’t running your filter regularly, or it’s not cleaning inefficiently and needs to be cleaned or backwashed, problems will arise.

6. You Didn’t Use Pool Floc Or Clarifier

Pool flocculant and pool clarifier are very similar and using either one can help clear up cloudy green water.

Flocculant binds to small particle impurities in the water, causing them to clump together and fall to the bottom of the pool. Once there, they can be removed with a skimmer or vacuum. 

Clarifier works to “clarify” the water (see what I did there). In all seriousness, clarifier works exactly the same as floc, except the clumps float on the surface of the water, allowing you to use a skimmer to pick them up, or let the pool’s filtration system do its job.

7. Your Chemistry Is Still Out Of Whack

Assuming your water was green, then restored, and then went back to green, that’s a strong indication you’re having issues with your pool water chemistry.

Water testing and staying on top of the appropriate chemicals will be needed to balance the water, including:

  • pH level: A pool’s pH level can make or break the water, and a properly balanced (neutral) pH level is imperative. The recommended range is between 7.2 and 7.6, with 7.4 being ideal. If the water drops below this range, it becomes acidic, and if it spikes above this range it becomes alkaline – both of which present challenges with water color (as well as more serious pool issues).
  • Chlorine level: Sanitizer must always be present in the pool, but too much chlorine can cause hazy green water, and lack of chlorine will be insufficient, making way for algae. The minimum level of chlorine should be 1.0 ppm, with 3.0 being the top end. Of course, if shocking the pool you’ll temporarily have higher levels present, and you should wait until the chlorine levels out before going swimming again.
  • Cyanuric acid: Otherwise known as pool stabilizer, CYA extends your chlorine’s lifespan, protecting it from the harmful UV rays of the sun. But if too much CYA is present, it will “lock” the chlorine molecules, and the chlorine will become ineffective. Ideally, you want CYA to be testing at 50 ppm. If too high, the only way to bring it down is to dilute the pool.
  • Total alkalinity: Alkalinity refers to the level of dissolved carbonates, bicarbonates, hydroxides and cyanurates in the water, and should be between 80 and 120 ppm. Falling below 80, you’ll end up with an acidic pool that can turn green, and going above 120 will cause a cloudy, alkaline pool that will be hard to bring the pH back down.
  • Metals: Metals in the water can also cause green water issues. Things like iron, copper, silver, magnesium, and manganese can be present and should be tested for. Copper especially can make pool water turn green as soon as chlorine is added due to the oxidation reaction between the two.

Furthermore, you may have heard about phosphates affecting your pool water quality. However, at low levels, they won’t compromise the integrity of chlorine so don’t be overly concerned with phosphates (and phosphate remover).

Consider The Nuclear Option

Unfortunately in some cases of green water, the pool can be too far gone to bring back to life and you’ll have to do a partial or full drain. But, as filling a pool skyrockets your water bill, this should always be a last resort. 

If you can still see the floor in the shallow end of the pool, it may have a fighting chance. Run the filter non-stop, brush and shock like there’s no tomorrow, and endlessly test and balance your water.

However, you also have to consider if your pool filter can handle the job. If it’s on the smaller side, gets overwhelmed by “thick” water, or is too noisy to run 24 hours a day, you may have to throw in the towel.

Additionally, stains from algae and other debris can be permanent on the pool’s finish. While you may be able to get rid of the green water color, the stains might have to be acid washed, which will require a full drain.

Green, Green, Go Away!

If your pool is still green after shock has been added to the water, fear not. There’s countless reasons why this may be happening, as evidenced above.

Equipping yourself with the right knowledge about green pool issues will help you diagnose, and ultimately, restore the water color so you can spend more time enjoying the pool, and less time fixing it.

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