Quick Dip: How to Shock Your Swimming Pool using Liquid Chlorine
Shocking your pool water is one of the keys to keeping your pool sparkling and ready to swim in. Failing to shock your pool water can lead to algae and bacteria build-up. This creates a swimming pool that is not only uninviting, but hazardous to pool patrons as well. Just because your water is clear, does not mean it is safe to swim in! This is why a high-quality pool testing set from LaMotte or Taylor is an essential part of every pool operator’s kit!
Shocking a pool with liquid chlorine or a granular pool shock kills or inactivates pathogens and algae. Shocking will also oxidize other unwanted materials inhabiting the pool water. By raising the chlorine level in the pool to the correct level, and holding it there for the prescribed amount of time, this effectively disinfects the water. This article covers shocking your pool with two of the most popular shock products on the market today – sodium hypochlorite (liquid chlorine pool shock) and calcium hypochlorite (granular shock).
Preparing to Shock Your Pool
- Know how many gallons of water your pool holds. Need assistance with this? Pentair has a handy online calculator that can tell you the volume of your pool.
- Using your pool testing kit, check your current chlorine level. This is important if you are attempting to bring your chlorine level up to an exact level. (More on the ‘advanced method’ later.)
- Before adding your pool shock, you must first make sure your water’s pH level is balanced. Using your test kit, ensure your water’s pH level is between 7.2 and 7.8. Why is this important? If your pH is out of range, it will greatly reduce the effectiveness of your pool shock. To learn more about water balance and how to achieve it, click here.
- Choose your pool shock. Two of the most popular options we carry are;
- Sodium hypochlorite aka liquid chlorine. This is one of the most commonly used sanitizers in the pool industry. Normally sold to consumers in gallon bottles, this high-strength product is easy to apply – as long as proper safety measures are taken! Our liquid chlorine is of 12.5% strength.
- Calcium Hypochlorite. This is a granular product that features a high level of available chlorine. (Arch Poolife TurboShock is of 75-78% strength.) This product is sold in easy to use single pound bags, or can also be found in larger pail quantities.
The Basic Method – Shocking by Following the Label Instructions
How to Superchlorinate your Pool with Liquid and Granular Chlorine
There can be a good bit of math involved in shocking your pool. If you want to get technical, the amount of chlorine already in your pool, the concentration of your chosen shock product and the volume of your pool all come into play. For many residential pools, or if you just want a ballpark estimation on how much pool shock you will need, simply follow the directions on the packaging. Often, it will look something like this.
- 12.5% Liquid Chlorine Pool Shock – Normal Dosage: 1 gallon of shock per 10,000 gallons of water.
- Shock Dosage: 2 gallons of shock per 10,000 gallons of water.
- Source: Champion Liquid Pool Shock instructions.
- 75-78% Calcium Hypochlorite Granular Pool Shock – Shock Dosage: 1 lb (bag) of shock per 10,000 gallons of water.
- Source: Arch Poolife TurboShock instructions.
In many scenarios, this should get you rolling. However, it is not the most precise option available. Below, we go into detail regarding the mathematical formulas used by Certified Pool Operators to ensure their pools and hot tubs stay clean and within their state’s code.
The Advanced Method – Shocking by Following Mathematical Formula
How to Superchlorinate your Pool with Liquid Chlorine (Sodium Hypochlorite)
Here is an example. If you have a 30,000-gallon pool with a current Total Chlorine (TAC) level of 3.0 ppm and a Free Chlorine (FAC) level of 1.0 ppm, how much 12.5% liquid chlorine/sodium hypochlorite would be needed to reach Breakpoint Superchlorination?(10.7 fl ounces of sodium hypochlorite = 1 ppm adjustment.)
- Using your pool water testing kit, find your Total Chlorine (TAC) and Free Chlorine (FAC) levels. For this example, the TAC = 3.0 ppm and the FAC = 1.0 ppm.
- Subtract your FAC from your TAC to find your Combined Chlorine (CAC) level. (TAC – FAC = CAC) For this example, 3.0 ppm – 1.0 ppm = 2.0 ppm.
- Use the formula below to calculate how much of a ppm increase you will need to add to reach Breakpoint.
- Combined Chlorine (CAC) x 10 – Existing Free Chlorine (FAC) = Adjustment Level
- 2 x 10 – 1 = Adjustment Level of 19 ppm
- Combined Chlorine (CAC) x 10 – Existing Free Chlorine (FAC) = Adjustment Level
- Finding the Amount of Chemical. We now need to find how much 12.5% Sodium Hypochlorite should be used to raise the PPM by 1. It takes 10.7 ounces of our 12.5% Sodium Hypochlorite to raise the PPM by 1 per 10,000 gallons.
- The unit we are measuring the volume of the pool by is 10,000 gallons. Divide the volume of the pool by 10,000.
- 30,000 Gallon Pool ÷ 10,000 gallons = 3
- To find the amount of 12.5% Sodium Hypochlorite to use to reach a breakpoint, use the following formula.
- Amount of Chemical x Pool Volume ÷ by 10,000 Gallons x Adjustment Level = Total to Reach Breakpoint
- 10.7 x 3 x 19 = 609.9 Ounces/4.76 Gallons of 12.5% Sodium Hypochlorite
The answer to this story problem is 4.76 gallons of 12.5% Sodium Hypochlorite. Although this calculation takes a while, it gives you a much more accurate chemical dosing measurement. This can possibly save you money by reducing waste.
BONUS: How to Superchlorinate in the case of an Accidental Liquid Fecal Release
How to Super Chlorinate your Pool to 20 PPM with Liquid Chlorine (Sodium Hypochlorite)
Here is an example. Your 30,000-gallon pool has an accidental liquid fecal release. Your pool has a Free Available Chlorine (FAC) level of 2 ppm. How much liquid chlorine/sodium hypochlorite would be needed to reach the mandated 20 ppm Superchlorination to respond to an accidental liquid fecal release? You will be using 12.5% sodium hypochlorite. (10.7 fl ounces of sodium hypochlorite = 1 ppm adjustment.)
- Test your pool water to determine the amount of free chlorine (FAC) in parts per million (PPM).
- Determine how many ppm you will need to increase the chlorine level to 20 ppm.
- Use the information on the product label or formula to figure out how much product will be needed to increase the amount of free chlorine by 1 ppm per 10,000 gallons of water. In the case of 12.5% sodium hypochlorite, this would be 10.7 fl ounces.
- Ensure your pH level is between 7.2 and 7.8. This greatly increases the effectiveness of the chlorine. If it is out of this range, it will lessen its effect.
- If you already know how much product it takes to add 1 PPM, you may skip this step. If not, here is how to calculate the amount of chlorine needed. It takes 1 ounce of chlorine in 7,500 gallons of water to equal 1 ppm. We will divide 30,000 gallons by 7,500 to get 4. It requires 4 ounces of chlorine to raise the parts per million of this example pool by 1. The pool already has a level of 2, so we will need to raise the level by 18 to reach our goal of 20.
- 4 ounces of chlorine x 18 ppm = 72 ounces. Since this product is 12.5% available chlorine, we will divide 72 by .125. This results in 576 ounces of sodium hypochlorite. 4.5 gallons of product.
- Broadcast the sodium hypochlorite directly into your pool water. Hold this level for approx. 16 hours to complete the super chlorination cycle at 20 ppm.
Quick Pool Shock Tips
- It is recommended that you keep personal protective equipment such as protective eye-glasses and gloves on hand.
- Wear closed-toe shoes and clothes that you don’t mind messing up as pool shock can quickly bleach clothing.
- As stated previously, always balance your pool’s pH level BEFORE shocking your pool.
- Make sure the shock product you are using is up to the task. Liquid pool shock (liquid chlorine) can degrade over time, so make sure your stock is fairly fresh. Granular shock products vary in strength. Make sure that your granular shock is of a high percentage.
About Us: Since 1982, Leisure Pool & Spa Supply has steadily grown to become one of the leading pool and spa service and supply companies in the Midwest United States. Under the leadership of Tim Yoder, and the rest of the Leisure Pool & Spa Supply staff, our company has grown to service virtually the entire state of Indiana and beyond. If you have any questions regarding your pool or aquatic center needs, do not hesitate to get in touch with us. We are always available via phone or email and look forward to assisting you. If you are looking to purchase products directly online, visit our online pool and spa supply store.