Sodium Thiosulfate Chemistry

Endless

Member
May 11, 2022
12
Colorado
I searched the threads for information on sodium thiosulfate, but did not find an answer to the questions of whether sodium thiosulfate produces ammonia and whether this ammonia, if produced, dissipates on its own. I use the chemical after having shocked the pool for a few hours (shock to about 7 ppm when my combined chlorine is .5ppm). In other words does sodium thiosulfate produce more chloramines after shocking?
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
21,420
Tucson, AZ
Pool Size
16000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Thiosulfate contains no amine (nitrogen) groups so how can it form ammonia??

Sodium thiosulfate is simply a reducing agent. It reduces chlorine to to chloride and it becomes oxidized to form sulfate. So the products of the reaction are chloride and sulfate. There are various reactions between thiosulfate and chlorine and so the reaction is not pH neutral.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
21,420
Tucson, AZ
Pool Size
16000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
It’s not a pool. It’s a spa. My neighbor has one but you really can’t treat them like you do pools. They are just really big spas.

Anyway, is it open to sunlight at all?

And, FYI, if you used CYA it would have a buffering effect on the active chlorine levels such that you would not have to worry about the effect on your liner or o-rings. Chlorine without CYA is incredibly harsh. It’s a common misconception but CYA is not just for UV protection. It’s also a chlorine buffer.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
21,420
Tucson, AZ
Pool Size
16000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
That’s not a great setup. You need a supplemental oxidation source as all of the chlorine you put in the pool is going to create CCs. And, because you’re not using CYA, the chlorine/nitrogen reactions are going to favor the formation of the nastier nitrogen trichloride rather than monochloramine. You are also going to build up persistent combine chlorine compounds that chlorine itself cannot oxidize. So unless you are dumping your water regularly, it’s just going to build up.

I would highly suggest, if at all possible, that you add an external UV sanitizer to the swim spas plumbing. It’s not necessary for disinfection but will help to breakdown bather waste when your FC is low so that it doesn’t all form CCs. Do NOT use ozone as you are in a confined space and that would cause a respiratory hazard.
 

Mdragger88

Bronze Supporter
TFP Guide
Jun 1, 2018
6,970
Hernando, Ms
Pool Size
26000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
We have a great guide u can follow
to care for your swim spa👇
 

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