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Updated on March 4, 2025
ljstevens0807@gmail.com
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March 4, 2025 at 3:37 pm
Q:

ClO2 for spa disinfectant and algae
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I have been thinking about switching to ClO2 for spa disinfection. Our spa started turning slightly green recently so I put in 50 grams for a 250 gallon spa per the spa guidelines. I was shocked when the spa turned bright green! Since there is visible algae, is that dosage sufficient. I repeated the dose and it did the same thing. Any feedback would be appreciated.

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KTLockhart
Keymaster
April 14, 2025 at 2:34 pm
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Hi there,

It sounds like you have significant algae build up, and no, the dose you have been using (5 PPM) is not going to be sufficient. The color you are seeing is the yellow from the ClO2 combined with the green from the existing algae. For a spa with less algae growth, a Shock treatment can be applied at 5 to 25 PPM, but because of the level of build-up (which will also be in the lines) our technician has recommended a complete change of the water.

They recommend cleaning all accessible surfaces with water, or water with a little vinegar. Refill the tub with clean water, then give it a low Shock treatment of 5 PPM to clean the lines. Afterward, continue as stated in the chart. Our tech recommends 3 PPM every few days depending on the level of usage.

You could do multiple Shock treatments at 25 PPM when algae growth is significant (for instance, if you can see a thicker green film or any large chunks that blow out of the jets when they are turned on) if you do not wish to clean the spa. But please be aware that you will need repeated treatments at 25 PPM in order to break down all of that visible growth.

There is more information on Pool and Spa treatment covered in our Hotel Industry brochure here, beginning on page 34. You will find specific Spa treatment directions on page 34:

https://safrax.com/wp-content/uploads/SAFRAX-CHLORINE-DIOXIDE-CLO2-HOTEL-INDUSTRY-2023-.pdf

Please reach out to support@safrax.com if you would like further support from our technicians.

Warm regards,
KT
Safrax.com

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