shocking with MPS and FC level

[anne]

If I have a bit over 0.5 ppm CC, and I shock with MPS to oxidize the nasites away, is the chlorine converted back to FC, or is it just gone?

I ask because usually my FC level is almost zero 24 hrs after adding a dose, but not today: My normal dosing is 1 tsp per person, sometimes 1.5tsp. Late wednesday night, I shocked and added my standard 1 tsp chlorine. Thursday night I measured nothing but added 2 tsp chlorine after two of us used the tub. Tonight (friday night) my FC was 5ppm! That is a full 24 hrs since the last dose. Maybe this happens more than I realize, as I do not check chlorine level all that often now that I know 1-1.5 tsp will result in 4-5 ppm after soaking. I usually just check it when I expect it to be zero so that I can see if there is any CC that would warrant a shock, or after shocking to ensure that my CC is gone.

Not that I'm complaining. I guess a good FC residual means my tub is pretty clean, right? It just seemed odd.

[tileman]

Anne, When CC is eliminated the rest of the dichlor left will become FC. So I guess to answer your question, that .5 CC is gone and is not converted to an additional .5 FC.
As far as your FC being 5ppm 24 hrs after adding 2 tsp of dichlor, that's a good thing and is not out of the ordinary for a well maintained spa.
I usually add 1.5 tsp after my soaking and it maintains a 2-3 ppm 24 hrs later.

[hottub.pool_boy]

It's gone. Only combined Bromine goes back to bromine after a shock, some is gassed off.

[Vinny]

I've read that if you shock the chlorine that's locked up will become free chlorine. I've also read where the CC is converted to it's basic elements and the chlorine that was locked up doesn't get converted back.

I seem to think that the 2nd scenario is correct. Reading my handy dandy Taylor reference book, it makes no mention that CC will be converted to FC ... of course in the new book I have (Nov 2004) they also say that MPS doesn't get rid of CC but in an older Taylor book (2003) they don't say that. I think it's a misprint in the newer book.

I also sometimes have a high chlorine reading 24 hours after adding chlorine. I attribute that to a "clean" tub that chlorine doesn't have much to do. I have added 4.5 PPM (3 teaspoons) after a soak and test 24 hours later and get possibly 2-3 PPM.

Of course your tub could have developed chlorine lock like mine ...

[pg_rider]

Don't some MPS shocks contain dichlor as well?  I think it's called "Enhanced Shock" or something.  So yeah, not only will it oxidize but it'll bump up your FC as well.  My FC is off the chart 30 minutes after adding 2oz of enhanced shock and takes a solid day just to go down to 5ppm...

[anne]

Thanks guys. I thought I had heard that the chlorine was just dissipated into its elemental parts, but I also remembered something about it "freeing up" chlorine from the organic matter. I'm going to assume that the chorine is gone.

My MSP is pure MPS- not enhanced.

What is chlorine lock? I have heard that phrase here, but never got the actual definition.

[hottubdan]

Where does this practice of adding x amount of chlorine per person come from?

The chemical manfacturers recommend adding x amount per gallon.

[tileman]

Where does this practice of adding x amount of chlorine per person come from?

The chemical manfacturers recommend adding x amount per gallon.

Uh, the Northman Style and the Vermonter Style. It can be found on rhtubs.com in the BBS section. It makes sense to me because how is the chemical manufacturer suppossed to know how clean/dirty each soaker is.

[Vinny]

Thanks guys. I thought I had heard that the chlorine was just dissipated into its elemental parts, but I also remembered something about it "freeing up" chlorine from the organic matter. I'm going to assume that the chorine is gone.

My MSP is pure MPS- not enhanced.

What is chlorine lock? I have heard that phrase here, but never got the actual definition.

Chlorine lock is when your chlorine doesn'r dissipate. It stays for days. I had it toward the end of last winter I kept putting in chlorine based on my usage patten and by the following weekend it was up past 20 PPM... never had to worry about bacteria though!!!

[Vinny]

Where does this practice of adding x amount of chlorine per person come from?

The chemical manfacturers recommend adding x amount per gallon.

The idea is to get the chlorine to a certain PPM reguardless of the gallons. It takes into account that a more people need more than a single person to get to the same PPM. Also takes into account other water or bather factors. Vermonter's idea (and Northman's too) is to add enough chlorine for at least a 3 PPM residue 20 minutes after adding, sometimes you need more to achieve it.

[anne]

Chlorine lock is when your chlorine doesn'r dissipate. It stays for days. I had it toward the end of last winter I kept putting in chlorine based on my usage patten and by the following weekend it was up past 20 PPM... never had to worry about bacteria though!!!

Right, but why does that happen? And then what do you do about it?

[MostlyLurkingGal]

I'd sure like to know about chlorine lock too...as I'm going on a week now of  not using my tub due to high HIGH chlorine count after shocking with what I now know was too much diclor. Was that a run-on sentence??

[Vinny]

Chlorine lock is when your chlorine doesn'r dissipate. It stays for days. I had it toward the end of last winter I kept putting in chlorine based on my usage patten and by the following weekend it was up past 20 PPM... never had to worry about bacteria though!!!

Right, but why does that happen? And then what do you do about it?

I have no clue! It happened, I used peroxide to neutralize the chlorine thinking it needed to be used up. It came back, went away for a while and then came back until I dumped the water.

MostlyLurkingGal, you can try to use either peroxide or buy chlorine neutralizer from a pool/spa store. Just be careful not to add too much, it will eat up any chlorine that gets put into the spa if the neutralizer doesn't get used up.

[tileman]

Chlorine lock is when your chlorine doesn'r dissipate. It stays for days. I had it toward the end of last winter I kept putting in chlorine based on my usage patten and by the following weekend it was up past 20 PPM... never had to worry about bacteria though!!!

Right, but why does that happen? And then what do you do about it?

I found this on a water chemistry site.
CHLORINE LOCK: If the level of cyanuric acid (stabliser) in the water is much over 80ppm, the chlorine becomes trapped and is unable to oxidise effectively. Despite being able to measure normal chlorine levels, the Redox potential is very low, indicating a lack of oxidiser. The only way to fix this is to drain some of the water and refill the spa. Care should be taken when using stabilised chlorine products (dichlor or trichlor) to avoid the level of cyanuric acid increasing too much.

SODIUM DICHLOR: A granular, stabilised organic chlorine compound providing 56% or 62% available chlorine that has a pH of 6.9. Used for regular chlorination. Should be used with caution for superchlorination as it can cause the stabiliser level to rise too high, resulting in chlorine lock.

I think I found what we're looking for
"It is extremely important to adjust the pH before adding the chlorine. When the pH is 8.0 the chlorine is only 20% effective and at a pH of 8.5 the chlorine is only 8% effective. Chlorine becomes overactive when the pH is lower than 7.0 ."

Your ph must have been below 7.0 when you superchlorinated and thus caused your chlorine to become overactive making the cyanuric acid levels  sky rocket causing a chlorine lock.
Here's another definition.
Chlorine Lock
A situation in which the cyanuric acid stabiliser has built up through continuous use of stabilised sanitisers. This slows down the rate at which hypochlorous acid forms in solution. There are two possible remedies. Either introduce fresh water into the spa or use unstabilised chlorine such as Sodium or Calcium Hypochlorite.

[anne]

Thanks for the info. I have not used the tub since last night, and I'll check the chlorine level tomorrow. Too lazy to do it now. I dont see how I could have added enough sanitizer to get the CYA level up that much. I hope not.

But it is still a new thing learned!