Does column pouring acid really work?
When you service pools, you’re constantly looking for tricks and hacks to save time and money. One trick that’s circulating among pool professionals is “column” pouring to save on time and balancers. Here we pick apart the claim with the science to determine if it's real or just a poolguy fairy tail.

What is Column Pouring?

As the name suggests, column pouring is where you add your liquid acid as a “column” – pouring it all in one spot (hopefully in the deep end of the pool). Liquid Acid is heavier than water, so when pouring it all one spot it sinks into a column.

This is opposed to the regular method of walking and pouring the acid around the perimeter of the pool.

What is it supposed to do?

The idea is that the Alkalinity will drop dramatically while having less effect on pH.

Being able to drop the alkalinity while keeping the pH the same would allow you to use less pH increaser to bring the pH up later. This would save a lot of work and money.

What does science say?

No explanation has been given to why this would be the case. Rather, this is based on personal observations. And unfortunately, personal observations can be misleading.

Law of Diffusion

First we have to understand Fick’s Law of Diffusion. This states that particles will tend to move from an area of high concentration to low concentration – until in a state of equilibrium.

This is experienced constantly in our everyday life. When someone is cutting onions, the irritants are first most intensely felt for the person cooking, then dissipates into the rest of the room until everyone’s eyes are tearing. If someone passes wind, the smell is worse for the person sitting next to them, then travels and dissipates to everyone in the room. Again, until everyone’s eyes are tearing.

Joking aside, this is a real phenomenon in science. And it’s happening in your pool as well.

When acid is added at a high concentration to one area, it will slowly dissipate as it is further dissolved by water – until it hits the point of equilibrium. Therefore, whether you pour all the acid in one spot or spread it around evenly, the net result should be the same.

But this diffusion takes time – and that might be where this myth came from.

When you spread the acid around the pool, it’s going to reach equilibrium much faster. But if you column pour it, you’re likely to reach equilibrium much more slowly. 

Remember, Alkalinity is a buffer. It helps the water resist a change in pH. So Alkalinity will likely be affected first before a change in pH will be registered. 

So if you’re a pool service operator and come back to test after column pouring, you might see the alkalinity decrease before the pH. But this doesn’t mean the pH won’t change – only that it will take longer to show the change.

What’s wrong with Column Pouring?

Column pouring doesn’t provide any benefits – at least not meaningful ones. But is there a downside?

There are two major problems with column pouring.

First, you’ll always be behind on balancing. This is because you won’t get accurate test results since the acid is still diffusing through the water. This will not only make it more difficult to balance, but you’re likely to waste more balancers. Rather than saving yourself, you’ll actually be costing yourself time and money.

Second, you’re putting the surface at unnecessary risk. Muriatic Acid is heavier than water. So if you pour in a column, you are effectively driving concentrated acid on the surface. 

Doing this occasionally won’t hurt anything – like giving a mild acid wash. However, continuing this pattern overtime can lead to etching and discoloration of the surface.

So is acid column pouring worth it?

No. Not only does it make it more difficult to balance pool water, it puts the surface of the pool at unnecessary risk. You’re much better off taking the time to dilute and pour the acid around the pool. 

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