Should I Drain My Pool To Get Rid of Algae?

If you’ve not used your pool for a while and ignored even an inch of algae, you might end up with a pool that is covered in green goo. Hold off on draining your pool out of disgust.

On average, you should not drain your pool to get rid of algae when you can use excessive pool shock and filtration to get rid of algae permanently. That said, partially draining the pool makes chlorine more effective at killing the algae.

In this article, you will learn every step required to get rid of algae in your swimming pool without draining any water. You will also discover how the process compares to refilling your pool. By the end, you will not only know the best course of action but also which decision is best for you.

Get the Algae in Suspension

If you’ve tried killing algae with chemicals, you might be frustrated because it keeps coming back, or the chemicals don’t seem to have any effect. This is because the algae lodged between pool tiles or clinging to the pool walls keep reproducing. So the first step is to make sure you get the maximum alga-kills per drop of algae-killer. For this, you can use a pool scrubbing brush.

Sepetrel Pool Brush is excellent for this and other pool cleaning tasks. It has a slight angle to it, which allows for clearing difficult corners of any stubborn dirt. Usually, the algae cling to the walls near the surface, which means you don’t need a corner-friendly brush. I just prefer getting one that I can use for the pool walls and the floor. Depending on the brush you use, you’ll get different volumes of the algae off the pool.

The more you remove from the walls, the less likely algae are to return. This is crucial to know because if you put in less effort at this stage, you’ll not be able to get rid of algae completely. A simple alga reproduction cycle shows that an inch of leftover alga can turn the whole pool green.

So the key point is that you have to take scrubbing as seriously as chemical dumps when you try to get rid of algae for good.

Shock the Pool

This step is not as shocking if you know that chlorine kills algae. You need to shock the pool and use Chlorine Shock to do it, even if you’ve previously used chlorine-free shock. Moreover, you need to make the shock far more intense and effective by following these specifics:

Shock the Pool at Night 

Algae find it hard to reproduce in the absence of sunlight. More importantly, chlorine remains in water far longer without sunlight zapping it out.  

Use Double, Triple, or Quadruple the Regular Amount

The greener your pool, the more chlorine it needs to kill the algae. At a minimum, you need double the volume of shock you’d normally use for your pool. When you use four times the chlorine, you can truly be sure all the algae will be dead. Be careful of inhaling chlorine fumes, though. Using a respirator can help avoid irritation.

Repeat the Cycle (Including Later Steps) 

Finally, you might need to re-shock the pool the next day just to get rid of every last alga in it. Don’t dump your entire shock supply in one go because some chunks of algae might need repeated exposure in order to die.

Run the Pool Pump for 8 Hours To Get All the Algae

The more your run your pool pump and filter, the more algae it grabs. You have to keep backwashing the filter if the dead algae form a very thick layer. After around 8 hours of running the pump, you’re free to re-shock the pool for peace of mind. That said, reshocking isn’t optional for some pool owners. And here’s how you find out if you’re one of them.

Keep running the pool pump until all the algae are caught in the skimmers or the filter. It goes without saying that you have to wash them away wherever they get caught. If you’re running the pump for over 24 hours and there are still green algae on the surface, you need to re-shock the pool with a higher chlorine quantity.

You will know when the algae are dead when the water is cloudy with a bluish tint. This is because dead algae will be in the water but in such a small quantity and so dispersed that you will not be able to see them. They turn gray when they are dead, which results in said bluish tint.

Add Pool Clarifier

Once the algae are dead, you need to focus on making your pool reusable. And that starts with making its water clear. Pool Clarifier, like the Amazon-exclusive Aqua Clear, can do this job relatively quickly. Alternatively, you can just adjust pool chemicals and keep running the water filter. It takes a lot less ‘adjusting’ if you get cloudiness out of the way first.

Adjust Pool Chemicals After Testing the Water Balance

Because pool chemistry is context-specific, you will need to test the water pH and chemical levels before you can even attempt to balance the pool chemicals. Fortunately, most pool chemical packages come bundled with testing strips. If you’re missing them from your pool kit, then you can get Health Metric Pool Testing Strips independently. Once the chemicals are balanced, you’re free to use the pool!

Drain vs. Shock – What’s Better To Kill Algae?

This process can seem lengthy and may make you wonder if draining the pool is better. According to my calculations, draining a hot tub to get rid of algae is feasible, but for family pools and even Olympic-sized pools, refilling the water costs more than shocking away the algae. To make the process faster, you can drain some of the water. This increases the concentration of chlorine in water because of lower dilution.

Final Thoughts

You can drain your pool if you’re too disgusted to clear it otherwise. But it is much more practical to use the method covered in this article. Above all, you need to use an algaecide on a semi-regular basis to get rid of even the smallest algae clump you see in your pool.

Jed Arnold

Jed spent every year from the ages of 15 - 22 as a Lifeguard (Red Cross) and ages of 17 - 22 as a Certified Pool Operator (CPO). Between working for over a dozen facilities and owning a pool, he carries over a decade of pool experience.

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