Pool Cloudy After Chlorine Shock – How to Fix It
Are you puzzled to see cloudy pool water after shock treatment? You might think that a straight chlorine shock would give you clear water straight away. It’s not always the case though.
However, some cloudiness after shocking doesn’t mean that there is a significant problem.
In fact, it’s a very common problem that can be fixed rather easily. After making a few adjustments, you will be able to get your pool water crystal clear in no time at all. So how do you fix milky pool water after a shock treatment?
Note: Has there been a heavy storm since you shocked the pool? If so, check out this guide on cloudy water after rain.
What causes the water to turn cloudy after shocking?
When you discover that your pool has turned green, one of the most popular ways to fix it is by performing a chlorine shock. This effectively sees a high dosage of chlorine added to your water to remove any algae or pollutants.
Normally, this will help turn your water clear in a few days – or so you would hope. Sometimes, the water may stay cloudy and murky. Even after it has been “shocked”. So why could this be?
There are several reasons why the water stays cloudy. These include:
- Contamination from debris
- Too soon after shocking
- Filtration issues
- High calcium levels
- High pH levels (if using unstabilised chlorine)
Let’s take a look at each of these in more detail, along with how to fix them.
Debris in your pool at the time of shocking is one obvious cause of cloudy or murky water. It’s worth double checking that your pool was relatively clean while shocking before moving on to the other potential causes.
Debris will add cloudiness to your water, and it will react with the chlorine you add as part of the shock treatment, which will lower its effectiveness as killing the chlorine and bacteria that it was intended for!
If this is the problem, make sure that you skim and vacuum the pool before your next shock treatment.
Too soon after shocking
The whole point of shocking is to kill algae and bacteria in your pool. The chlorine you added as part of the shock treatment does this effectively - but it can’t magically make these microorganisms disappear. Their ‘dead bodies’ - so to speak - are still floating in your pool and need to be removed.
It’s your filtration system's job to remove these dead organisms from your water. It will take your filter some time to clear out the junk from your water - give it at least a few hours, overnight is better.
If you’ve waited a day and the water is still cloudy, your filter may be playing up, and this could be the cause of your murky water.
Check the cartridge or filter media in your filter to make sure that it isn’t gunked up and is working freely. Take a look at the troubleshooting section of your filter manual for more advice.
High Calcium Levels
A high concentration of calcium in your water (determined by your hardness) can lead to cloudiness. How does this relate to shock treatment?
Well, if you happen to be using calcium hypochlorite (Ca(ClO)₂) to shock your pool, you could be adding enough calcium to the pool to lift the hardness to the point where scaling, calcium deposits, and subsequent cloudiness could be an issue.
For a typical shock treatment with calcium hypochlorite (using about 100g per 10,000L), you will add about 20 grams of calcium, which will lift the calcium hardness by 2 ppm. This may not sound like much, but calcium builds up in your pool over time, only leaving when you drain some water and refill with fresh water.
If you have a hard water supply, this could be the problem.
Keep your calcium hardness under 400 mg/L by testing monthly and following this guide on reducing calcium hardness.
High pH Levels with Unstabilised Chlorine
The effectiveness of your chlorine shock will depend heavily on your pH if you are using unstabilised chlorine.
As your pH heads further and further above 7.5, the effectiveness diminishes greatly. Keep your pH at around 7.2 - 7.6 before shocking with unstabilised chlorine and remember that adding chlorine temporarily increases pH, so the lower the pH is, the better.
If you shocked at a high pH, your chlorine won’t have killed all of the algae and bacteria in your pool, which can mean that the water is still cloudy.
Note that this is only true for unstabilised chlorine, which is why the stabilised version is highly recommended.
I’ve tried the above and my pool is still cloudy - what do I do?
If none of the above seem to be the cause of your cloudy water, all is not lost!
You can still clear up the cloudiness by adding a clarifier to your pool. These are inexpensive, easy to add, and will clear your pool quickly.
They work by clumping the individual particles suspended in your pool together, making them heavier so that they are more easily caught by the filter, or settle to the bottom of the pool where they can be vacuumed out.
It’s good to always keep some clarifier on hand for situations like this.
At the end of the day, seeing cloudy pool water after a shock is frustrating. But some due diligence will fix the issue without any major dramas.
Regularly checking your filters and removing debris will make a big difference to the state of your pool – before or after you shock it.
It’s also worth keeping on top of your water chemistry (especially the pH and calcium hardness) before you shock your pool, otherwise your efforts may be wasted.
With a bit of extra care upfront, getting a crystal clear pool will be much easier!
A chemical engineer by trade, Louis is committed to debunking myths in the pool industry by explaining the underlying chemistry and making it accessible to all.