0.25 M Sodium Thiosulfate solution

This is a simple, convenient way to neutralize a bleach solution. This 500 mL bottle is concentrated to 0.25 M, which makes the dosage nearly 1-to-1 for neutralizing most household bleach products (typically 7.5%).

This chemical is very safe for use in the aquarium, and makes bleach-treated water safe for inhabitants (as it neutralizes chlorine).