Oxalic acid is an efficient and affordable solution for aquarists looking to reduce water hardness, provided that calcium content is the primary issue.
Procedure
The process requires some patience as the chemical reaction takes time, and the water needs to stabilize afterward.
- Preparation: Fill a large tub or container with the water you intend to treat.
- Addition: Prepare a solution of oxalic acid. Add it slowly while stirring constantly until the water reaches a $pH$ of approximately 4-5.
- Aeration: It is crucial to aerate the water vigorously for 12-24 hours. This step removes the large amounts of $CO_2$ released during the reaction.
- Precipitation: Let the water rest completely for at least one hour. The calcium will precipitate and settle at the bottom as a white powder.
- Collection: Carefully tap the soft water. Although the white powder at the bottom is harmless, you should avoid transferring it into your aquarium.
The resulting water is now very soft and can be used pure or mixed with tap water to reach the exact hardness required for your fish.
