Is there a minimum level of free chlorine required to work correctly?

[duganderson]

I have a smarter spa salt water generator and I can adjust the low and high range of chlorine in the tub (I confirm this with Taylor test). I add bleach after every use to ensure my free chlorine does not drop below the minimum I set.

If I set the minimum to a low level like 0.5 or 0.25 and the chlorine never drops to zero, is the chlorine still effective at killing bacteria and processing waste at low levels like 0.25 (as long as it does NOT drop to zero) OR is there a minimum level of chlorine required for the chlorine to be effective?

Would a Nature2 stick help a this lower range OR not as long as the Chlorine does not drop to zero?

(this is a bit more of a theoretical question because I know most people are not in a position to be able to manage the low range of chlorine on an ongoing basis)

 

[Texas Splash]

You generally keep the FC balanced to the current CYA in your tub as noted on the FC/CYA Levels. Whenever you go below that minimum number, you run the risk of algae, especially in a hot tub with the elevated temps. Tubs often times have a CYA in the ~30 range, maybe a little higher depending on what sanitation was used, so the FC is often times in the 3-6 range. But the sticky below goes into that a little more.

How do I use Chlorine in my Spa or Hot Tub?

If you have a question about any information within this Sticky, please start a new thread for yourself where you will receive very quick responses to your specific questions. Thank you! Introduction There are two main things to consider when maintaining your hot tub water, Water Balance and...

www.troublefreepool.com

 

[Oly]

Here is an old thread but posts #2 and #4 go into detail regarding your questions. Chlorine and MPS in my spa?

 

[5tan]

Water Treatment and Testing | Healthy Swimming | Healthy Water | CDC

www.cdc.gov

Free Available Chlorine Germ-Killing Timetable
E. coli 0157:H7 (Bacterium)	less than 1 minute
Hepatitis A (Virus)	approximately 16 minutes
Giardia (Parasite)	approximately 45 minutes
Cryptosporidium (Parasite)	approximately 15,300 minutes (10.6 days)

• Times based on 1 ppm free chlorine at pH 7.5 and 77°F (25°C)
• These disinfection times are only for pools and hot tubs/spas that do not use cyanuric acid. Disinfection times are longer in the presence of cyanuric acid.

It would be interesting if they could publish the same at various other levels of FC such as 3, 6, 10, 20.

To speed up the germ kill times:
1) Increase your FC (most spa manufacturers recommend no lower than 3ppm FC, an equipment max of 10-20, and a soaking max of 6).
2) Decrease your pH (lowest recommended is 7.2, but 7.6 is reportedly the most comfortable for human skin/eyes).
3) Decrease your cyanuric acid (by law in most North American provinces and states, indoor spas must have ZERO cyanuric acid. There is a set fine for having an above-zero CYA level).

If your source water is full of germs (bacteria, viruses, parasites), then you'd want to always hold a 6ppm FC level, 7.2pH, and 0 CYA. This ensures maximum germ killing power.

The forum enthusiasts here recommend 20-40ppm CYA when using a liquid bleach (incl. pool chlorine) maintenance method. Just know that the more CYA you have, the lower the effectiveness of the free chlorine. You may want to add CYA if you want to make the chlorine less harsh on your skin and swimwear (in terms of fabric strength as well as color).

If you've ever dunked a piece of stainless steel into a cup of bleach, you'll have noticed that it eats the steel. I suspect having a 20-40 CYA level and reducing the chlorine's strength can help extend the life of the spa's metallic components.

The mineral ions released by the Nature2 should enhance the germ-killing power of the water, in theory at least. I use Nature2, Spa Marvel, and Ahhsome Weekly Conditioner, but I chlorinate my water as if I didn't have these things. I just consider them extra insurance.