Bleach and sodium thiosulfate

[slosoak]

I work for a maintenance company and we use filter socks. We would spray clean then soak in a dilute bleach solution. Afterwards we would add sodium thiosulfate crystals to neutralize the bleach then soak in freshwater. We have been doing it this way for years. When we did it this week after adding the sodium thiosulfate and mixing ,a strong rotten egg odor occurred. What could have caused this? At another site I would mix the crystals in solution beforehand and use the liquid to neutralize the bleach. When the container was empty I noticed a rotten egg smell also. The crystals are stored as airtight as possible.
Mike

 

[lapin]

Acid mixed with sodium thiosulfate can cause that smell

 

[slosoak]

I was told that if the concentration of bleach was high enough it could cause hydrogen sulfide. This was from the thiosulfate manufacturer