Hard water has a high pH, with larger amounts of minerals like calcium in it. In some situations, hard water is not desirable. This is particularly true in fish aquariums, where some fish species are not accustomed to hard water. Water can be softened using a water softening system, or it can be done using natural ingredients like peat moss. Natural methods are effective and tend to cost less than buying a softening system, but they also take some time and a bit of work.
Boil water in a kettle and pour it over your peat moss. Allow it to sit overnight. This will encourage the peat moss to soak up as much water as possible. If you desire, you can add the water to the aquarium to help soften the water.
Fill a nylon bag or cheesecloth full of peat moss and hang it in your aquarium. It will start softening the water right away.
Test the pH of your water. If it is at a desired level, leave the peat moss bag in. Check your pH regularly to ensure the peat is still working. If the water starts to harden, replace the bag with a new one. If the pH isn't soft enough, you can add more peat moss to the bag.