# Thread: How much chlorine/oxidizer to use after soak?

1. ## How much chlorine/oxidizer to use after soak?

This is a great forum. I am so pleased I found this site as well as poolspaforum.

I've been following waterbear's bromine for beginners at both sites. It has left me with a few questions. One of which is how much, if any, oxidizer/chlorine do I use after a soak? I have a 300 gallon spa for which I am using bromine following the three step process.

Thanks for any help.

2. ## Re: How much chlorine/oxidizer to use after soak?

I believe chem geek already answered your question on the other forum. There is no definite answer like 1+1=2. Adding oxidizer after a soak has so many variables to consider that giving one answer doesn't work. Two adults who bath in the nude with a shower before the hot tub will give a different result than 2 teenage girls with swimming suits and makeup on. Your test kit will tell you what to add before and after your soak.

I guess it would be neat if Pool Math had an "if then" formula at the bottom for this topic. For instance, plug in 2 bathers, nude, 30 minute soak, then add this much oxidizer. Wouldn't be perfect, but I'm sure it would get you in the ballpark.

3. ## Re: How much chlorine/oxidizer to use after soak?

The rough rule-of-thumb that applies for soaking in a hot (104ºF) spa that has no ozonator is that every person-hour of soaking needs roughly 3-1/2 teaspoons of Dichlor or 5 fluid ounces of 6% bleach (3-1/2 fluid ounces of 8.25% bleach) or 7 teaspoons of non-chlorine shock (43% MPS) to oxidize bather waste. With an ozonator, the amounts could be roughly cut in half. These quantities are independent of spa size and are the same regardless of whether you use chlorine or are activating bromine from a bromide bank.

For bromine, you add whatever amount is needed after a soak so that you still have a residual after 24 hours. The rule-of-thumb above is just that, a rule-of-thumb, and people sweat somewhat different amounts. In between soaks, bromine tabs can maintain a residual bromine level. If you have an ozonator, then it may be able to maintain a residual from the bromide bank, possibly enough to not need bromine tabs.

4. ## Re: How much chlorine/oxidizer to use after soak?

Tx for the replies. It is very appreciated.

5. ## Re: How much chlorine/oxidizer to use after soak?

On a related note, anyone know how much 8.25% bleach to use for my weekly spa shock? I just picked up a 3 pack at Costco. Waterbear's post states that for a 250-300 gal spa shocked with 6% bleach, a person needs 3/4 cup. If u could enlighten me that would be great.

6. ## Re: How much chlorine/oxidizer to use after soak?

You would just scale it so 3/4 * (6/8.25) = 0.55 so roughly 1/2 cup of 8.25% bleach should be fine. That's around 9 ppm FC in 300 gallons.

7. ## Re: How much chlorine/oxidizer to use after soak?

Tx a bunch for the quick response!

8. ## Re: How much chlorine/oxidizer to use after soak?

One thing I have noticed is that bathers come in different sizes, and the amount of chlorine required after a soak definitely scales with the size of the bather. There's probably a smartphone app that analyzes a picture of the bathers and gives you a recommended chlorine dose, but I haven't found it yet

Worst case bather load (hunting buddies & tub too hot) seems to consume about 16 oz of 10.5% bleach for 3 bather-hours before leaving me with a few ppm of FC. I generally add 8 oz, wait a few hours then add the other 8 oz, but IIRC the initial reaction (to monochloramine ?) is pretty fast so I guess waiting only a half hour (or dumping it all in at once) might be better.

9. ## Re: How much chlorine/oxidizer to use after soak?

bridgman, so you are saying that your hunting buddies are eating up too much chlorine? Aren't they bathing in no scent soap, shampoo, and using scent blocker clothing to shoot da thirdy pointer? LOL. Your tub picture looks great!

10. ## Re: How much chlorine/oxidizer to use after soak?

The rough rule-of-thumb is 5 fluid ounces of 6% bleach per person-hour so for 10.5% bleach and 3 bather-hours this would be around 8.6 fluid ounces so somewhat more than half what you are using. Big sweaty hunting buddies -- have to note that increases chlorine demand

It's not a problem for you to add the entire chlorine amount at once rather than in doses. It will just have the reactions go faster but you'd want to keep the cover off to outgas some of the chloramines. I also presume you have no ozonator, otherwise the chlorine demand from bather load would likely be less, though the chlorine demand in between soaks would be higher.

11. ## Re: How much chlorine/oxidizer to use after soak?

I noted the yellow caution at the top of this thread before posting this, but since this was my original thread/post, I can proceed fwd. Not to mention, this next question is related.

Regarding the post-soak addition of sanitizer (not the weekly shock), if I use my spa 2x in one day (more than just 1x), do I still add after each soak, or do you TFPers add at the end of the day or when it will not be used anymore that day? For instance, I just used it w/ my kids. My spa is bromine sanitized. I added my Dichlor accordingly after our soak (2 tsp). I use Dichlor b/c I think it is the easiest since I can leave that next to the spa w/ a measuring tsp. vs. chlorine which I would have to walk to the garage to go get, etc. We may go in the spa again later. Got me thinking it seems odd to repeat this same cycle again if it is going to be used later; thought that it would be better to do when the spa would not be used anymore today.