How Much Bleach To Use Daily Or After Soak?

[Venams]

OK So I have my hot tub completely balanced. PH around 7.5 TA about 70 and 50 PPM Borates. I've been using dichlor for about 2 weeks and my CYA should be around 30ppm or a little higher.

TUB is 450 gallons.

So I shocked to about 9ppm FC and next day was 8ppm so chlorine demand is 12%

My tub is currently at 4ppm and I was going to soak (just myself) today for an hour.

SO;

1) About how much Clorox (8.25%) do I need to add per day to keep tub in the 4-5ppm FC range (if no-one using tub)

2) how much chlorine should I add after my 1 hour soak today (FC at 4ppm before soak)

[chem geek]

It sounds like you don't have an ozonator given your low chlorine demand, correct? It sounds like you are losing very little chlorine per day in between soaks so would only need to add 0.5 ppm FC or perhaps 1 ppm FC per day at most and could probably go every other day if you wanted to. The Pool Calculator says that 1 ppm FC in 450 gallons is 0.7 fluid ounces so thats around 1-1/2 tablespoons or around 4 teaspoons.

If one person soaks for one hour in a hot (104ºF) tub then that needs around 3-1/2 fluid ounces of 8.25% bleach to oxidize the bather waste. However, the tub may not be that hot if you are in it for an hour so you might need less. Just add that amount and see what you end up with 24 hours later and adjust accordingly. You'll soon get a feel for your chlorine demand after your soak and in between soaks. Every spa is a little different.

Also, most people prefer to soak with a lower chlorine level, around 1-2 ppm FC, so that they smell less chloramines during their soak, but that's up to you. If you don't mind, it's not a problem. With the CYA in the water, chlorine's strength is moderated and 4 ppm FC with 30 ppm CYA at 104ºF is roughly equivalent to 0.5 ppm FC with no CYA.

Note that you'll need to watch your pH as it may rise, especially if you use aeration jets. You may need to get your TA down lower which acid addition to adjust pH will likely do. Just see how things go, but transitioning from Dichlor to bleach will have a change in pH behavior since Dichlor is net acidic while bleach is not.

[Venams]

Thanks Chem Geek.

I keep my tub around 98 or 99 (thin skin!) which is plenty warm for me.

I do have an OEM ozonizer on my spa which is verified as working.

[chem geek]

Well you ozonator must be pretty weak or not operating for very long each day because usually one sees a higher chlorine demand in between soaks due to ozone oxidizing chlorine. Consider yourself lucky. With a more typical ozonator, 24-hour chlorine demand can go from 20-25% up to 40-50% or even higher. On the plus side, the chlorine amount required after a soak with such an ozonator would be cut roughly in half.

In your case, you should err on the high side by starting with the recommended rule-of-thumb for dosing and then cut back if it keeps too high a chlorine level 24 hours later.