Using Sodium Thiosulphate to neutralize Chlorine

[niccumec]

@Randy Holmes-Farley
I am looking to sterilize SW for culturing phytoplankton. I have run across discrepancies on amount of Sodium Thiosulphate solution (10% w/v) to use to neutralize the chlorine. Below is the recommendation I got from Grok which shows 2.68 ml to neutralize 50 ppm chlorine in 4 liters of SW. Using ChatGPT the recommendation was 1 ml. Being a 3x discrepancy, I thought I’d get a real chemist’s input. It has been way too long since I took Chemistry in school.

Grok basis:
[ 2Na₂S₂O₃ + Cl₂ + H₂O → Na₂S₄O₆ + 2NaCl + 2HCl ]
“This shows that 2 moles of sodium thiosulfate neutralize 1 mole of chlorine. However, in practice, we use a simplified ratio for aquarium applications, where 1 mg/L of chlorine requires approximately 1.34 mg/L of sodium thiosulfate (anhydrous) to neutralize it, based on the molecular weights and reaction stoichiometry.
From this, 1 mole of sodium thiosulfate neutralizes 4 moles of chlorine.”

Does this look correct?

Chat GPT used this balance (which ends up using only 1 ml to neutralize 50 ppm Cl in 4 L):

Which is correct?

Also, I thought I bought Sodium Thiosulphate from LoudWolf, but the chemical shows Na₂S3O4, not Na₂S₂O₃…. Could this be a typo - see bottle label. I don’t want to add the wrong chemical!!!

 

[mook1178]

Sodium thiosulfate will pull the oxygen out of the water.

If you want to remove chlorine, bubble the SW for 24 hours.

 

[Randy Holmes-Farley]

Don't believe the google search AI on this topic. It is all over the map based on false internet info and false claims about what forms the sulfur takes after reaction. It's largely driven by student homework problems that ask folks to balance equations, I suspect, without regard for whether that is actually the reaction taking place.

Sodium thiosulfate is Na2S2O3.

Na2S3O4 appears to be a typo that pervades the internet. I do not believe there is any such chemical that is available for purchase.

The thiosulfate chlorine reaction is 1:4 moles. It can be written many ways, such as:

4 NaClO + Na2S2O3 + 2 NaOH → 4 NaCl + 2 Na2SO4 + H2O

 

[mook1178]

Sodium thiosulfate will pull the oxygen out of the water.

If you want to remove chlorine, bubble the SW for 24 hours.

I was thinking sodium sulfite... Ignore my reply about oxygen

 

[ron_pinctadamaxima]

@Randy Holmes-Farley
I am looking to sterilize SW for culturing phytoplankton. I have run across discrepancies on amount of Sodium Thiosulphate solution (10% w/v) to use to neutralize the chlorine. Below is the recommendation I got from Grok which shows 2.68 ml to neutralize 50 ppm chlorine in 4 liters of SW. Using ChatGPT the recommendation was 1 ml. Being a 3x discrepancy, I thought I’d get a real chemist’s input. It has been way too long since I took Chemistry in school.

Grok basis:
[ 2Na₂S₂O₃ + Cl₂ + H₂O → Na₂S₄O₆ + 2NaCl + 2HCl ]
“This shows that 2 moles of sodium thiosulfate neutralize 1 mole of chlorine. However, in practice, we use a simplified ratio for aquarium applications, where 1 mg/L of chlorine requires approximately 1.34 mg/L of sodium thiosulfate (anhydrous) to neutralize it, based on the molecular weights and reaction stoichiometry.
From this, 1 mole of sodium thiosulfate neutralizes 4 moles of chlorine.”

Does this look correct?

Chat GPT used this balance (which ends up using only 1 ml to neutralize 50 ppm Cl in 4 L):

Which is correct?

Also, I thought I bought Sodium Thiosulphate from LoudWolf, but the chemical shows Na₂S3O4, not Na₂S₂O₃…. Could this be a typo - see bottle label. I don’t want to add the wrong chemical!!!

I've been working in a pearl oyster hatchery for over 20 years now. My recipe for chlorine neutralization for plankton culture is: dissolve 55g of sodium thiosulfate in 1 liter of distilled water as stock solution. Use same amount as the amount of bleach (5% chlorine) used. Eg. If I add 100 ml of bleach to sea water, I also add 100 ml of thiosulfate stock solution.

 

[acro_lover]

Hi @Randy Holmes-Farley , i need your advice. I have made myself 0.5L of DIY potassium iodine not realising that this will last me forever :)
Is Sodium thiosulfate considered reef safe and do you think is a good idea to add a little to stabilise? My iodide recepe is 4g in 0.5L ro water. I was thinking of adding about 0.25–0.5 g Sodium thiosulfate to my iodide solution? What do you think?

 

[Randy Holmes-Farley]

Hi @Randy Holmes-Farley , i need your advice. I have made myself 0.5L of DIY potassium iodine not realising that this will last me forever :)
Is Sodium thiosulfate considered reef safe and do you think is a good idea to add a little to stabilise? My iodide recepe is 4g in 0.5L ro water. I was thinking of adding about 0.25–0.5 g Sodium thiosulfate to my iodide solution? What do you think?

I don’t know for sure that it prevents air oxidation, but it probably would. I personally would not add it, but if I did I’d add a lot less than you suggest. Maybe 1/10th.

 

[acro_lover]

@Randy Holmes-Farley , it seems that your DIY 2 part recipe has been deleted from reefkeeping.com ( the page doesnt exist). Do you have another link to it? I re-read it from time to time. Also wanted to check what are the pros and cons about dosing sodium bicarbonate vs sodium carbonate. Thanks

 

[Randy Holmes-Farley]

With any lost articles, one can put the link into the way back machine:

Internet Archive: Digital Library of Free & Borrowable Texts, Movies, Music & Wayback Machine

archive.org

In this case, that gives:

https://web.archive.org/web/20250126152252/https://reefkeeping.com/issues/2006-02/rhf/index.php

The main difference between bicarbonate, carbonate, and hydroxide is pH.

Also note this thread:

DIY Balling Method Recipe

The Balling DIY supplement recipe utilize a 1:1:1 dosing ratio to maintain proper alkalinity. For instance, if you require 50 mL of the alkalinity solution, you should also add 50 mL of Calcium and Balling. Alkalinity (Choose One) : Option 1: Soda Ash Add 375 g soda ash to enough RO/DI to...

www.reef2reef.com

 

[acro_lover]

Amazing, thank you very much. Happy Reefkeeping!

 

[DCR]

Just a warning that many municipal water districts have converted to chloramines instead of chlorine and thiosulfate is not effective against chloramine.

 

[Randy Holmes-Farley]

Just a warning that many municipal water districts have converted to chloramines instead of chlorine and thiosulfate is not effective against chloramine.

It is effective, it just leaves the ammonia in the water, which may or may not be a concern depending on how it is used.

 

[acro_lover]

Hi @Randy Holmes-Farley , would you share some experience :) I am experimenting with some vitamin mixes. Want to see if the corals will benefit somehow. Have you ever used potassium sorbate? Would you say is reef safe? Planning to add something like 250-300mg to my 0.5L vitamin mix to prevent microbial growth. What do you think?

 

[Randy Holmes-Farley]

Hi @Randy Holmes-Farley , would you share some experience :) I am experimenting with some vitamin mixes. Want to see if the corals will benefit somehow. Have you ever used potassium sorbate? Would you say is reef safe? Planning to add something like 250-300mg to my 0.5L vitamin mix to prevent microbial growth. What do you think?

How much of this mix would you be adding to what size tank and how often?

 

[acro_lover]

How much of this mix would you be adding to what size tank and how often?

Starting daily dose for 900L aquarium will be 4ml daily for the vitamins.
And i am also working on diy amino acid, that one will be 1ml daily dose to 900L. They are both dissolved in their 0.5L dark glass bottles and will be kept in a fridge.
However it will take me a while to finish the finish each bottle therefore i thought i will add a little bit of potassium sorbate.

 

[Randy Holmes-Farley]

I think that will be fine. The resulting concentration of sorbate in the tank will be so far below it’s needed concentration to inhibit bacteria that it’s not a concern.

It is broken down by bacteria, so it won’t accumulate in the tank.

 

[acro_lover]

I think that will be fine. The resulting concentration of sorbate in the tank will be so far below it’s needed concentration to inhibit bacteria that it’s not a concern.

It is broken down by bacteria, so it won’t accumulate in the tank.

awesome, thanks. Is there anything better that you would use or stick to the potassium sorbate? Thanks

 

[Randy Holmes-Farley]

awesome, thanks. Is there anything better that you would use or stick to the potassium sorbate? Thanks

I don’t really know what’s best is a situation like this. Sorry.

 

[acro_lover]

I don’t really know what’s best is a situation like this. Sorry.

Understood. Thanks for your help. Happy Reefkeeping