How much Shock ?

[jbequer]

Sorry about asking a silly question, but I am new to the Hot Tub seen and am really trying to get this chemical thing down.
I am in the process of purging with Ahh-Some , draining and refilling. I have owned my Hot Spot Rhythm for a month. My water was looking pretty nasty and took the advice of others to drain . I know that because the spa is new it is a good idea to drain after a month or so.

My question is this, how much Dichlor should I use ( tbs vs tsp) as a once a week shock for 375 gallons ? I normally use about 1/2 teaspoon per person after use but I am confused as how to shock. Usage is about 2 to 3 people three times a week , and of course the occasional 4 to 5 people once every two weeks. What should my PPM be after Shocking ?

I am using Aquafinesse, Dichlor , Clarifier as needed, Anti Foam as needed. For some reason, I lost control after larger use dose for a day. My first thought is that I wasn't shocking enough. I learned about shocking three weeks into ownership which was probably to late.
One other problem is that my wife is very sensitive to chemicals , which is one reason for the Aquafinesse and Dichlor vs MPS.
Please help, it can't be this difficult to keep clean..

Thanks.

[jbequer]

Any advice?

[kporter]

My initial reaction is 1/2 teaspoon per person is not cutting it. (I would be going tablespoon) Your total chlorine was most likely through the roof with very little to no free chlorine.

Porter

[chem geek]

If you use the proper amount of chlorine after each soak and you maintain some chlorine in between soaks, then you should not need to shock regularly.

With no ozonator, every person-hour of soaking in a hot (104ºF) spa needs round 3-1/2 teaspoons of Dichlor or 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 required amounts may be half or less.

It does seem that you aren't adding enough chlorine.  1/2 teaspoon would handle less than 10 minutes of one person soaking.

[jbequer]

When you say 3.5 tsp per person, what is it for two people, 7 tsp ? Not sure I follow, at what point of bathers to I get to a point where too much Dichlor is added ?
2 add how much?
3 ?
And so on.

I was adding no more than 4 tsp even after 4 bathers.

[amy2421]

When you say 3.5 tsp per person, what is it for two people, 7 tsp ? Not sure I follow, at what point of bathers to I get to a point where too much Dichlor is added ?
2 add how much?
3 ?
And so on.

I was adding no more than 4 tsp even after 4 bathers.

I am no expert because we just got our tub 2 weeks ago, but the dealer told us to put in 1/2 tablespoon of Chlorine Granules per person per 20 minutes of use. There are only 2 of us so we put in one tablespoon after using the tub and then run the jets for 20 minutes with the air valves closed. We're monitoring the PH and alkalinity and chlorine with test strips and getting the water tested weekly. Once per week we are told to put in 2.5 tablespoons of chlorine, 1 tablespoon of spa shock and 4 caps of Stain & Scale.

After we got our PH within the proper level, we dumped in a container of Spa Solution which is supposed to help maintain balanced levels and clarity.

[chem geek]

The real rule is to add whatever amount of chlorine is necessary after a soak so that you still measure a residual of chlorine (say 1-2 ppm FC or so) 24-hours later.  If you have an ozonator, then the amounts needed will be about half or less of what I indicated.  With no ozonator and with hot (104ºF) water, the 3-1/2 teaspoon per person-hour will be about right.  Two people for one hour would be 7 teaspoons, BUT there's no way you could soak in 104ºF for one hour so since the actual temperature will likely be less then the dosage amount would be less.

1/2 tablespoon per person per 20 minutes works out to (3 teaspoons/tablespoon)*(1/2 tablespoon)*(60 minutes/hour)/(20 minutes) = 4.5 teaspoons per person-hour.  That's probably higher than needed, but roughly in the ballpark of what I've been saying.  Again, the real rule is to test your chlorine level 24 hours later and adjust your dosing accordingly.

If you dose after each soak AND also dose to maintain a chlorine residual (say, 2 ppm FC) in between soaks, then there should be no need for weekly shocking.

I was adding no more than 4 tsp even after 4 bathers.

So there is no wonder why you ran into problems.  You are adding way too little chlorine.  4 bathers for 20 minutes (1/3 hour) would be 4*(1/3)*3.5 = 4.7 teaspoons of Dichlor, if there is no ozonator.

[jbequer]

Thank you, where is this formula from ? Is it acurate?

[Dr. Spa™ Ret.]

While traveling down a path in the jungle, you come to a folk in the road. You know that one way leads to a tribe friendly natives, the other to a tribe of cannibals, that will immediate eat you. The Friendlies always tell the truth, the Cannibals always lie. Both tribes dress exactly the same.  At the fork in the road is a native. What one single question can you ask him to ensure your safety?

[Quickbeam]

While traveling down a path in the jungle, you come to a folk in the road. You know that one way leads to a tribe friendly natives, the other to a tribe of cannibals, that will immediate eat you. The Friendlies always tell the truth, the Cannibals always lie. Both tribes dress exactly the same.  At the fork in the road is a native. What one single question can you ask him to ensure your safety?

Are you hungry?

[Dr. Spa™ Ret.]

oops

[chem geek]

Thank you, where is this formula from ? Is it acurate?

It's based on observation of hundreds of posts on multiple spa forums over many years.  It's only a rough rule-of-thumb.  As I wrote, the real rule is to add whatever amount is necessary to have a small chlorine residual 24-hours later.  If you are adding too much, then you won't have enough chlorine and if you are adding too much your chlorine level will be too high.

I originally came up with a rough estimate based on known sweat and urine amounts and the amount of chlorine necessary to oxidize that bather waste and then tweaked that based on the observations on the forums.  Roughly speaking, every person-hour of soaking in a hot (104ºF) spa requires 9 grams of chlorine (as ppm Cl₂) whereas in swimming pools the rough rule-of thumb is that every person-hour requires 4 grams of chlorine.  This assumes fairly clean people (i.e not sweaty or dirty getting into the water) and only light-to-moderate swimming activity in the pool case (i.e. not competitive swimming).

[lehacf]

What would happen if I put too much of MPS shock and how to determine that?

[chem geek]

MPS needs to be measured through special tests since it will show up looking like Combined Chlorine (CC) in the regular DPD chlorine test or as Free Chlorine (FC) in the FAS-DPD chlorine test if any regular chlorine is present.  There are MPS test strips that supposedly show MPS levels separate from chlorine and for FAS-DPD chlorine tests there is the Taylor K-2042 to test MPS separately from chlorine.  If you didn't have much chlorine in the water, then you can reasonably assume that what you are measuring is just MPS.

So the simplest thing to do is to use your chlorine test and look at total chlorine (FC+CC) and if it's high after adding a lot of MPS then that's likely MPS that is left.  Chlorine will get used up more quickly than MPS since chlorine reacts with some chemicals (like ammonia) that MPS does not (or does very slowly).  Unless the MPS level is very high (say above 20 ppm), I wouldn't worry about it.  It will get used up with the bather waste from soaking in the spa.

[lehacf]

Thank you!

Couple more questions. What specifically happens when MPS gets "used up with the bather waste from soaking in the spa". Does it get attached to bather waste and become a larger particle that can be captured by the filter or something else happens to it?

How many bather/hours (if such term exists) can be gained from typical 400 gallon tub between each refill with proper chemicals application?