Here's why:
* Natural Habitat: Many tropical fish originate from rivers, lakes, and streams in areas with low mineral content, leading to soft water.
* pH Level: Soft water generally has a lower pH level (more acidic), which is often ideal for tropical fish.
* Mineral Content: Hard water has a high mineral content, which can affect fish health, especially in the long term.
However, there are exceptions:
* Some tropical fish species, such as African cichlids, prefer hard water with a higher pH level.
* Certain species, like discus, thrive in slightly acidic water with a medium hardness level.
It's crucial to research the specific water parameters (pH, hardness, etc.) required for each species you're considering keeping.
Here are some general guidelines:
* Soft water: 0-5 dGH (degrees of general hardness)
* Medium hardness: 6-12 dGH
* Hard water: 13-20 dGH
You can adjust the water hardness and pH level through water changes, adding specific chemicals, and using filtration systems. It's also essential to monitor these parameters regularly to ensure optimal conditions for your fish.