How To Use Muriatic Acid To Lower Your Pool’s Alkalinity

Muriatic acid is one of the best products to lower both your pH and total alkalinity.  It is one one of the most corrosive forms of acid and its uses go from swimming pool care to metal and brick cleaning.  Great care must be taken to ensure you're safe around this kind of acid.

Some have said that by leaving the pH alone, your pool's alkalinity will decrease on its own.  This is false.  The fill water in Albany, OR where I was the pool operator and had taken care of dozens of pools, had a pH of 8.2 and an alkalinity of 30 ppm.  Only adding sodium bicarbonate to raise the alkalinity, or muriatic acid to lower it, would have any affect on the alkalinity.  Rain did as well, but that proves the statement below. 

We live in a physical world.  Newton's first law states that "every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force."  This is true in physics and true with pool water chemistry. 

20 Mule Team Borax will effectively increase your pH, while grocery store baking soda  is absolutely ideal for raising the total alkalinity.  Your can use certain products from your grocery store with great confidence.  Never fall for the "professional strength product"  or "especially for pools" routine.   It's called marketing for a reason.   

How To Use Muriatic Acid To Lower Your Pool’s Alkalinity

Low pH and High Alkalinity

This seems to be a common theme with many pool owners.  What should I do I when I have low pH and high alkalinity?  If I add muriatic acid, it lowers the alkalinity, but my pH goes too far down.  It's the yo-yo effect that can drive you crazy.  There's an easy solution and it almost FREE.  Yeas I said almost, because the free thing I'm talking about it AIR.  That's right.  All of this stuff around us, and we're going to use it to our advantage. 

So how is this accomplished, you might be asking?  Well, if you have an air compressor or Shop Vac, you're in business.  You see, introducing air into your pool, through the products already mentioned, or by turning on water features such as water falls or slides, will produce millions and million of bubbles in your pool.  These bubbles reach the surface and POP.  This popping releases CO2 (carbon dioxide) and will raise the pH without much of anything happening to your alkalinity.

So get out your Shop Van or air compressor and go to town on raising your pH after you've lowered your alkalinity

How To Lower Pool Alkalinity

Another great product that pool supply stores have is called pH Decreaser, which is Sodium Bisulfate.  This can effectively lower both the pH and alkalinity, but we're talking about muriatic acid, and that's something you probably have on hand.  It's actually less expensive than pH Decreaser and works just as well as dry acid for lowering your pool's alkalinity.  

Think Safety

While muriatic acid is great to lower the alkalinity in your pool, it is one of the most caustic acids in the world, so care must be taken in order to safely lower your pools' alkalinity.  You'll need:

  • Goggles
  • Safety glasses
  • Long sleeve shirt and long pants
  • A 5 gallon bucket
  • Plastic or wooden stir stick
  • Large glass measuring cup
  • Muriatic acid

Test Your Pool Water

The key is to test test test your pool water.  It makes it much more difficult to determine how far to lower the alkalinity without knowing the starting point.  I recommend and use the Taylor K-2006 pool test kit.  It's the best on the market and the most accurate.  Test strips are alright in a pinch, but we want accuracy.  

How Much Muriatic Acid Do I Need?

Now here's the funky part, so to speak.  What we're going to do is use muriatic acid to lower BOTH our pH and alkalinity, then RAISE our pH.  I know it might seem a bit odd, but believe me, this method works the best.  As a general rule, we're going to use 15 oz. of muriatic acid to lower our pH 0.2 per 10,000 gallons.  Another great resources you might consider is the pool calculator

Add The Muriatic Acid

Adding your muriatic acid straight into the pool might cause the acid to settle to the bottom and that's something we don't want.  So let's grab out bucket and begin.

  • Test your pool water to know where your alkalinity currently is
  • Get your safety gear on
  • Fill your bucket up 3/4 with pool water
  • Fill your measuring cup with the appropriate amount of muriatic acid
  • Pour the acid into the bucket and gently stir with your stir stick
  • Slowly and gently pour the mixture around the perimeter of the deep end
  • Turn the pump motor on and allow the system to filter for 8 - 10 hours
  • Come back and retest both the pH and alkalinity
  • If your pH has decreased to our goal of 7.0 - 7.2, use the the aeration method of a Shop Vac, air compressor, slide. water fall, or other water features you may have
  • Make another chemical adjustment if needed and repeat the process until your pool's alkalinity is in the proper range

This might seem a bit tedious, but because muriatic acid lowers both the pH and alkalinity, we should have a dual-pronged approach.

IMPORTANT: It's much safer to always add your chemical to the water, NOT the water to the chemical.  

Allow The Muriatic Acid To Do Its Job

Properly managed pool chemistry will reduce the need for constantly adjusting your alkalinity.  Just remember, if your pool's alkalinity starts to creep back up again, a little muriatic acid and the right method can help you get things back to normal and enjoying your pool once again. 

What Other Visitors Have Said

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