how to calculate pool chemicals
How to calculate how much pool chemicals you need to use:
Did you know that adding chemicals into your swimming pool is like a big science experiment? You have to measure out the right quantity of pool chemicals, and add them in the right order — or else something can go wrong. But, if you manage to add the correct amounts, then your pool will become sparkling clean and ready to jump into!
That said, how much of each chemical should you be adding to your swimming pool? The answer to that can be quite tricky, so let’s take a look at our guide on how to calculate pool chemicals:
Step 1: Get the measurements of your pool
First, you should know your pool volume — it’s extremely important in calculating the number of chemicals you need to add to your pool water.
If you want to find the volume of your pool, there are a few measurements you need to find, namely: width, depth, length, radius, and pi constant (3.14).
Make sure that all the measurements have the same unit of measure (i.e., meters or feet)
With these measurements, you should be ready to make any kind of calculation you need to help you find the volume of your pool — it’s time to tap into your old geometry lessons! Remember the following calculations:
For irregularly shaped pools, this can get even more difficult to calculate — but it’s still possible to do. In this situation, try to break your pool into different sections. Find any “standard” circular, square, or rectangular shapes you can find, and make those into sections. This can result in as many as 5 to 6 different sections.
From there, use the appropriate calculations mentioned previously to determine the volume for each section before adding the numbers together.
Now you have to find how many gallons your pool is holding. Remember that each cubic foot of water consists of 7.5 gallons of water. So, after using these equations, multiply the number you get by 7.5 — resulting in the total volume of your pool.
Step 2: Check the dosage recommendations on the label
Next, check your pool chemicals. It’s important to always follow the product’s given instructions when using chemicals, so take a look if there are any dosage recommendations on their labels.
If it has a label, then it’ll typically include dosage information — which is the standard amount of chemical you need to adjust a standard amount of pool water. It usually looks something like this: “1.5 oz per 10,000 gallons of water to raise pH by 1 ppm.”
If not on the label, check your test kit (which should come with a guidebook).
If you bought your pool chemicals in bulk, then there’s a possibility that there is no label. In that case, refer to a water chemistry adjustment guide table — like this one — to find the recommended dosage.
Step 3: Calculate how much you need
Once you have the recommended dosage, this amount needs to be converted to be specific to your pool’s needs.
You already have your pool volume, but now it’s time to find the amount of chemical change that needs to take place in your pool water. This means testing your pool with your test kits — like this HCT Pool & Spa 5 in 1 — to find your pool’s current chemical levels. From there, refer to the appropriate levels to know how much change needs to be made:
Remember what the correct levels should be:
From here, refer to your chemical dosage information and pool volume. Calculate how much you need to produce the desired chemical change to your pool water.
To do this, you need to find the following values:
Use these values in the following equation:
Chemical dosage for your pool = Pool Factor Change Factor Amount of Chemical (on chemical dosage label)
Sounds complicated? Don’t worry, it’s easier than you think. To help you understand, let’s use an example:
Let’s say you need to lower your pH levels by 1 to get it from 8.6pH to 7.6pH. The directions on your HCT dry acid say that you need 10 grams per 1,000 gallons to decrease pH by 0.5. With simple math, you can see that you need 20 grams of HCT dry acid to get the desired result. And, let’s say your pool’s volume is 14,000 gallons. Here’s what the formula will look like:
Chemical dosage for your pool = [14,000 gal ÷ 1,000 gal] [8.6pH ÷ 7.6pH] 10 grams of HCT dry acid
= 14 (Pool Factor) x 1.13 (Change Factor) x 10 grams
= 158.2 grams!
This means you need 4.5 pounds of HCT dry acid to raise the total alkalinity in your 14,000-gallon pool by 20 ppm.
Step 4: Measure out approximations
If you’re unsure of your calculations, then you might want to measure out approximations and “sneak up” on the water chemistry level you’re trying to hit. This means breaking down the total amount you need to add (based on your calculations) into smaller doses, and adding them little by little to your pool.
After each dose, you’ll have to wait for the chemical to mix in fully, then retest the water to see if the chemistry levels are close to your target levels. This will help you slowly work up to the right level, while also avoiding overshooting the mark — which is harder to fix!
Step 5: Use a pool calculator
If all else fails, and you’re unsure if you’re calculating the right amounts, you can always use online pool calculators to double-check your math. This one at poolcalculator.com has all the options you need to calculate chlorine, pH levels, total alkalinity, and calcium hardness.
To use calculators like these, all you need to do is enter the measurements of your pool, as well as the current chemistry values of your pool water. Then, add in your target values, and the calculator will churn out the right amount of chemical you need to add.
As with any science experiment, you have to approach pool chemistry with a lot of precision — so learning how to calculate pool chemicals and finding the right quantity to add to your water is a must in maintaining your pool!