Draining Above-Ground Pool Because of Algae: Good or Bad Idea?

Draining Above-Ground Pool Because of Algae

As unpleasant as it is to think about, there may come a time when the clear and pristine water in your above-ground pool turns green because of algae.

I’m not accusing you of being lazy; sometimes life just gets in the way. You could be genuinely busy or on vacation. Perhaps there was an equipment malfunction; the timer broke or the pump stopped working. It could be some external factor like having some unruly “friends” over and them deciding to use your pool like a toilet, or the result of a week’s worth of rain.

In any case, your pool has now turned an unsightly green with a foul odor to match how it looks. Most people’s first instinct is to drain a green pool and refill it with freshwater. However, not only is this a huge waste of water, but it can damage your above-ground pool and create more problems than it solves.

If the water in your above-ground pool has turned green because of algae, you need to shock the pool with chlorine. This will not only kill the algae, but can get the dead algae out of the water as well. Generally speaking, if you can fix your pool problem without draining the water, then that is the option you should take. Draining your pool can cause the liner to get damaged beyond repair.

Why draining the pool is not a good idea

There are two things you need to know to better understand why you don’t have to, nor should you drain the pool water:

  1. Chlorine is incredibly effective at disinfecting water.
  2. An empty pool is susceptible to damage from the elements.

To elaborate on the first point, do you know what wastewater treatment plants use to sanitize the sewage water? They use a form of chlorine. That is the same chemical we use in our swimming pools to keep our pool water clean and pristine. If chlorine can clean sewage, it can keep our pool water clean no matter how dirty it seems.

The second point is that draining the water can damage your pool. First, many pools are designed such that they are at their most structurally stable when they are full of water. Water is really heavy and can keep the pool in place and provide outward pressure so the walls don’t collapse when there is a strong external force pushing inward.

Another issue is that the vinyl liner will get damaged beyond repair when it dries. As it dries, it will shrink and become brittle. Even after you fill it with water again, it doesn’t return to the same suppleness it once had, and you basically should just replace it because it has lost its elasticity.

What you should do instead: shock the pool

If you’ve never heard the term before, “shocking the pool” refers to adding a large amount of chlorine to your pool for a brief period of time.

This high concentration of chlorine will kill all the algae and bacteria in the pool given sufficient quantities and time. And if it doesn’t, you just keep shocking it until the water clears up. It’s quite simple in concept.

How much chlorine do you need to add? That depends on how much algae is in your pool and how large your pool is. No one can say for sure unless they can test your pool. However, the more algae there is and the bigger the pool, the more chlorine is needed.

Now I’m sure there is some expert out there that can explain to you how they can mathematically calculate exactly how much chlorine is required per gallon of pool water and how much you need to adjust it by based on the pH levels and so on, but thankfully you can just ballpark it and get great results so that’s my preferred approach.

How to shock your above-ground pool to get rid of algae

Check the pump and filter

Ensure the water pressure is as it should be. Clean the filter. If you have a sand filter, it could take up to a week or more for the pool to completely clear. That’s assuming it’s even in working order.

Test the water

Use a water testing kit. Determine if the chlorine level is at zero. If it isn’t, don’t shock the pool until it reads zero. Since we’re ballparking how much chlorine to add, this just makes things easier. Also make sure the pH is normal or on the low side (chlorine will spike it up).

Add liquid chlorine

It’s finally time to shock the pool. My preferred shock is to just use liquid chlorine.

I don’t like to use tablets because they can cause problems. Whether it sinks to the bottom or floats along the surface, if it stays in contact with the liner for too long it can damage it. Liquid chlorine is much easier to spread around evenly.

Buy one of those reusable 2.5 gallon jugs of liquid chlorine at a pool store for this next step.

Now, if your above-ground pool is round and 24 feet or bigger, then add two of the 2.5 gallon jugs of liquid chlorine.

If your pool is round and 21 feet or smaller, then just add a single 2.5 gallon jug of liquid chlorine.

Now run the pump to circulate the chlorine around the pool and leave it running for 12 hours a day. This also lets the dead algae settle on the bottom which sets you up perfectly for the next step.

Vacuum to waste

After the pump has been turned off for a few hours, vacuuming the bottom of the pool to waste will get rid of the dead algae settled there and send it into the yard. Even if you can’t vacuum to waste, vacuum it anyway.

Now clean the filter again. Is your pool clean and pristine? If it’s still a bit green, test the water again and wait for the chlorine to reach close to zero, and repeat the steps all the way until you’re back to this step.

Not recommended: draining your pool to clean algae

I am adding in this section because I know some people want to clean their pool this way. You do this at your own risk.

As a reminder, draining your pool can cause the pool liner to shrink. Once this happens, it won’t stretch back again and become susceptible to splitting or pulling down from the pool wall. You’ll essentially need to replace it with a new liner. You’ve been warned!

Empty the pool the night before

Your pool is most likely to shrink once the sun is up and starts heating up your pool liner. To minimize the damage, empty the pool the night before so that you can wake up early in the morning and get to cleaning before the temperatures rise.

Start scrubbing

After the pool is drained, there will be stubborn algae and debris still lingering on the liner. Care must be taken not to scratch the liner with brushes or poles.

If you need to enter the pool at any point during the cleaning process, be careful not to step on limbs, toys, rocks, or any other protruding object that could puncture the liner.

Remember to work quickly and to start filling up the pool with freshwater ASAP. Once the sun comes up, it’s game over if your pool still isn’t filled with water.

Work quickly

One day is all it takes for the liner to shrink, so the pressure’s on. That’s also why I don’t recommend this step; cleanup can take longer than usual, the urgency may cause you to do a poor job and you can make mistakes, and you can just run out of time and now you need to replace the liner.

I recommend just shocking the pool instead. The cost of the chemicals required to shock the pool will be less than the cost of replacing the pool liner if you mess up.

Photo Credit: Clean Pool & Spa