Last Updated: June 29, 2022

Pool Alkalinity Calculator

Written By: Pool Care Guide

We highly recommend using a pool alkalinity calculator to estimate the correct baking soda dose because incorrect doses can have dramatic and unfortunate results. If the baking soda dose is too high, the raised total alkalinity will reduce the acidity and cause a contaminated cloudy calcified pool. If the baking soda dose is too low, the pH can easily drop and the water will become too acidic. This increased acidity will damage the pool and its equipment.

A pool’s total alkalinity is how we measure its ability to resist acidification. Total alkalinity is increased by adding sodium bicarbonate (baking soda) to water. When we add sodium bicarbonate to water, a process called hydrolysis (Hydro = Water, Lysis = cut) separates it into its constituent ions of sodium (Na+) and bicarbonate (HCO3-). 

The sodium diffuses throughout the pool and is irrelevant to the water’s total alkalinity while the bicarbonate stabilizes pH levels through a condition called chemical equilibrium.

What is the recommended pool alkalinity PPM?

The recommended alkalinity PPM is between 80 and 120 parts per million (PPM), and 100 PPM is ideal. 

Reference Chart for Raising Alkalinity

Whenever you add pool chemicals, initially add less than you need. It’s always easier to add chemicals into the pool than it is to reduce them.

If you are already familiar with the process of raising your pool’s alkalinity, you can use the chart below to find how much baking soda you need to add to bring pools to the 100 PPM ideal.

Baking Soda Dose Reference Chart for Lowering Alkalinity

Reduce Alkalinity PPM by8,000
Gallons
10,000
Gallons
12,000
Gallons
14,000
Gallons
16,000
Gallons
18,000
Gallons
20,000
Gallons
Reduce 10 PPM1 lbs
4 oz

1 lbs
10 oz

1 lbs
15 oz

2 lbs
4 oz

2 lbs
9 oz

2 lbs
14 oz

3 lbs
3 oz

Reduce 20 PPM2 lbs
9 oz
3 lbs
3 oz
3 lbs
13 oz

4 lbs
8 oz

5 lbs
2 oz

5 lbs
12 oz

6 lbs
6 oz

Reduce 30 PPM

3 lbs
13 oz

4 lbs
13 oz

5 lbs
12 oz

6 lbs
12 oz

7 lbs
11 oz

8 lbs
10 oz

9 lbs
10 oz

Reduce 40 PPM5 lbs
2 oz

6 lbs
6 oz

7 lbs
11 oz

8 lbs
15 oz

10 lbs
4 oz

11 lbs
8 oz

12 lbs
13 oz

Reduce 50 PPM6 lbs
6 oz

8 lbs9 lbs
10 oz

11 lbs
3 oz

12 lbs
13 oz

14 lbs
6 oz

16 lbs

Reduce 60 PPM

7 lbs
11 oz

9 lbs
10 oz
11 lbs
8 oz

13 lbs
7 oz

15 lbs
6 oz

17 lbs
4 oz

19 lbs
3 oz

If your alkalinity PPM is slightly higher than the 80 - 120 range, it should still be fine. Environmental factors will naturally bring it down. 

If your alkalinity is 150 or more, your pH is likely high as well. While we don’t want to enjoy a leisurely swim in a pool of acid, some acid is necessary for the health of your pool. Without it, calcium scales will start lining your pool walls.

Sometimes acids are described as molecules that steal electrons. Those are called Lewis acids. Most of the time, we are talking about “hydrogen donors,” and those are called Bronsted-Lowry acids. 

Our alkaline substance, probably bicarbonate, pairs up with hydrogens and becomes the weak carbonic acid. When in water, carbonic acid breaks down into H20 and CO2. 

With this in mind, you can reduce your alkalinity by adding acid to the pool. 

Okay, that sounds kind of dangerous. To be honest, it can be. You need to take precautions and know to work with acid safely. You need to wear gloves, goggles, and covering clothes, the acids should be diluted, and you need to keep people out of the pool.

Below, there are two charts listing doses of acid doses. Do not add doses of both acids. Choose one or the other. We recommend sodium bisulfate because it is much safer.

Option 1: How Much Sodium Bisulfate (Dry Acid)

Sodium Bisulfate (Dry Acid) Dose

Reduce Alkalinity PPM by8,000
Gallons
10,000
Gallons
12,000
Gallons
14,000
Gallons
16,000
Gallons
18,000
Gallons
20,000
Gallons
Reduce 10 PPM

1 lbs
4 oz

1 lbs
10 oz

1 lbs
15 oz

2 lbs
4 oz

2 lbs
9 oz

2 lbs
14 oz

3 lbs
3 oz

Reduce 20 PPM

2 lbs
9 oz

3 lbs
3 oz
3 lbs
13 oz

4 lbs
8 oz

5 lbs
2 oz

5 lbs
12 oz

6 lbs
6 oz

Reduce 30 PPM

3 lbs
13 oz

4 lbs
13 oz
5 lbs
12 oz
6 lbs
12 oz

7 lbs
11 oz

8 lbs
10 oz

9 lbs
10 oz

Reduce 40 PPM

5 lbs
2 oz

6 lbs
6 oz
7 lbs
11 oz

8 lbs
15 oz

10 lbs
4 oz

11 lbs
8 oz

12 lbs
13 oz

Reduce 50 PPM

6 lbs
6 oz

8 lbs

9 lbs
10 oz

11 lbs
3 oz

12 lbs
13 oz

14 lbs
6 oz

16 lbs

Reduce 60 PPM

7 lbs
11 oz

9 lbs
10 oz

11 lbs
8 oz

13 lbs
7 oz

15 lbs
6 oz

17 lbs
4 oz

19 lbs
3 oz

Option 2: How Much Muriatic Acid (Liquid Acid)? 

Muriatic Acid (Liquid Acid) Dose

Current Alkalinity1,000 Gallons5,000 Gallons10,000 Gallons15,000 Gallons20,000 Gallons
7.6 - 7.81.25 oz6 oz12 oz18 oz24 oz
7.8 - 8.01.50 oz8 oz16 oz24 oz1 qt
8.0 - 8.42.5 oz12 oz24 oz1.25 qts1.5 qts
8.4+3 oz16 oz1 qt1.5 qts2 qts

How to Manually Calculate the Baking Soda Dose

You don’t need to know the math and the reasoning behind it. Still, it might be helpful or fun to understand the cogs of how we are calculating all of this. If it doesn’t interest you, here is everything you need to manually calculate how much baking soda you need to reach 100 PPM.

Please Note (1 Gallon = 128 Fluid Ounces)

  • Step 1: Divide the desired PPM increase by 1,000,000
  • Step 2: Multiply the answer by your pool’s total fluid ounces
  • Step 3: Divide by .9586 (Converts fluid ounces to ounces)
  • Step 4: Divide by 16 (Convert ounces to pounds)
  • Step 5: Divide by .56 (Account for the additional sodium mass)

Example: Let’s increase a 10,000-gallon (1,280,000 ounces) pool’s alkalinity by 10 PPM

  • Step 1: 10 / 1,000,000 =.00001
  • Step 2: .000011,280,000 =12.8 Fluid Ounces of Bicarbonate
  • Step 3: 12.8/.9586 =13.3528 Fluid Ounces to Ounces 
  • Step 4: 13.3528 / 16 = .8346 ounces to pounds
  • Step 5: .8346 / .8346 = 1.49 Pounds of Baking Soda

That’s the basic math. You should have what you need to calculate your dose manually.

Baking Soda PPM vs. Alkalinity PPM

When a chemical is added to a solution, we use the formula above to calculate the PPM. As it is, this PPM formula will not tell you the baking soda dose that you need. That said, we can make it work with a few modifications. 

First, let’s break down the effect that a dose of baking has on the alkalinity of a pool. When we understand that, we can reverse the process, choose the desired increase of alkalinity, and work our way up to the near-exact dose of baking soda that we need.

Removing the Sodium

Baking soda is a chemical compound called sodium bicarbonate. One part of the compound is alkaline. The other part is not. If we run the PPM equation without isolating the alkaline portion of the compound, we will inflate the end result.

Sodium bicarbonate is water-soluble which means water breaks the bonds between the sodium and the bicarbonate. The sodium that breaks away is inconsequential to the pool’s alkalinity. For this reason, we need to dismiss it from our alkalinity calculations. The bicarbonate is important because it interacts with the H2O to create the alkaline buffering solution needed to stabilize pH levels.

If we’re going to calculate the pool’s alkalinity, we need to remove the mass of the sodium from the baking soda in our PPM calculation. Sodium bicarbonate has a density of 2.2 g/cm3, and sodium has a density of .968 g/cm3. That is a mass reduction of 44%, so that’s what we’ll take away from our baking soda. If we multiply the weight of the sodium bicarbonate (baking soda) by .56, it will give us the weight of the bicarbonate.

Converting Ounces to Fluid Ounces

Now that we have the weight of the bicarbonate, we need to convert its weight. Fluid ounces and dry ounces have two different values. If we want to know the true ratio, we need these values to match. Fluid ounces are 95.86% lighter than dry ounces, so we multiply the weight of the bicarbonate’s dry ounces by .9586 to convert the measurement.

Find the Ratio and the PPM

If you divide the bicarbonate’s fluid ounces by the fluid ounces of the water, the answer will be the bicarbonate-to-water ratio in decimal format. In other words, that tiny number represents how much bicarbonate you have for every single molecule of H2O. 

That number should be significantly less than 0. Otherwise, we aren’t talking about a pool of water. Depending on the number, you would have a pool piled with bicarbonate salt or a slush.

If you times that number by 1,000,000, it will show you how many molecules of bicarbonate you have for every 1,000,000 molecules of H2O.

If we put all of the steps together, the Alkalinity PPM equation looks something like this.

If we multiply the constants, we can reduce the formula to something a little more manageable.

Since we know the math, we can flip it around to find the dose. This solution to this formula will give you the amount of baking soda in pounds. If you want the answer in ounces, just times the solution by 16. 

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