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Septic System No-Nos: Using Pool Chlorine

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Septic tank no-nos: using pool chlorine

Aerobic septic systems use chlorine in the wastewater cleaning process, and a common question we get from aerobic system owners is whether or not they can use swimming pool chlorine tablets. The answer is no. Chlorine tablets for swimming pools are not designed to treat wastewater — only calcium hypochlorite tablets have been approved by the EPA for use in aerobic systems.

Pool chlorine is ineffective and dangerous

Here’s what the Texas Commission on Environmental Quality (TCEQ) says about it at TCEQ.com:

“When disinfection of secondarily treated wastewater effluent is required and you are using chlorine tablets, it is important that you use a chlorine tablet that is made from calcium hypochlorite and is certified for wastewater disinfection by EPA. They are very reactive and will kill 99% of the bacteria present in the effluent within 10 minutes. Follow all warning and precaution statements of the chlorine tablet manufacturer to protect yourself and the system equipment.

WARNING: DO NOT use swimming pool chlorine tablets in your disinfection system. The chlorine in these tablets are made from trichlorisocyanuric acid. Swimming pool tablets dissolve more slowly than calcium hypochlorite and do not thoroughly disinfect the effluent. Additionally, there is a danger of explosion using swimming pool tablets since the tablets will release an explosive gas called nitrogen chloride due to the fact that they are not totally immersed in water at all times while in use. They are not approved by EPA for wastewater effluent disinfection.”

What if I’ve used the wrong chlorine in my septic tank?

If you’ve used swimming pool chlorine tabs in your septic tank, remove the tabs from your chlorinator and clean it out well (see our video on cleaning your tablet chlorinator). Then add the correct tablets. Be careful not to mix the two types of tablets — this can cause explosions.

Where can I get the right chlorine tabs for my aerobic system?

You can buy buckets of tablets at the Van Delden office, or at any Home Depot or Lowe’s. Just make sure you’re getting tablets that are made from calcium hypochlorite and are EPA-certified to treat wastewater.

Tips on aerobic system care

Aerobic systems are more complex than their standard cousins, and require more and different care. To learn more about aerobic systems and how to keep yours working efficiently, download our free guide to Living with an Aerobic Unit and Spray Field.


For 80 years, Van Delden Wastewater Systems has withstood the test of time as the leading Wastewater System company, providing San Antonio, Boerne, and the surrounding Texas Hill Country with services you can count on now and in the future. 

Call us for any of your wastewater systems needs and let our professionals help you with your septic installation and maintenance requirements: 210.698.2000 (San Antonio) or 830.249.4000 (Boerne).


2 thoughts on “Septic System No-Nos: Using Pool Chlorine

    • I don’t know the technicalities of the chemical/biological repercussions, but I’m sure it would kill off some of the bacteria in the tank temporarily until it the bacteria has a chance to re-populate.

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