The way to lower hardness is by mixing hard tap water with a form of pure water such as reverse osmosis water. A half and half mixture will reduce the hardness by half.
I would research the fish you are interested in on https://www.seriouslyfish.com/knowledge-base/
This will tell you the type of water the fish need, the temperature the fish need, whether they need fast or slow flowing water, suggested tank mates and any other specific needs. For example, hillstream loaches need very fast flowing water, cooler temperatures than most fish need, and a lot of algae to feed on which a new tank is unlikely to have grown yet.
I would research the fish you are interested in on https://www.seriouslyfish.com/knowledge-base/
This will tell you the type of water the fish need, the temperature the fish need, whether they need fast or slow flowing water, suggested tank mates and any other specific needs. For example, hillstream loaches need very fast flowing water, cooler temperatures than most fish need, and a lot of algae to feed on which a new tank is unlikely to have grown yet.
