Most of the information presented on the Internet says Celestial Pearl Danio prefer soft water parameters. I’m not so sure that is true. Perhaps since many other nano fish come from soft water locations it is just assumed that CPD’s also prefer their water on the soft side.
Shortly after the Celestial Pearl Danio was introduced to the hobby, there was great concern that the little fish were going extinct in the wild. With that concern, a survey of the collection locations for CPD’s was conducted. Mr. U Tin Win made notes and took samples of the water during the survey.
Tin Win reports the water where these fish are found is crystal clear with a pH of 7.3 and the conductivity of 250 micro siemen. The pond bottom is covered with sand. The area is mostly grassland and rice paddies, so the ponds are open to the sun and filled with a rich variety of aquatic plants.
Now it’s tricky to give an exact water hardness equivalent for a conductivity of 250 microsiemens (µS/cm) because:
- Conductivity measures all dissolved ions: This includes those that contribute to hardness (calcium, magnesium) but also others like sodium, potassium, and carbonates.
- Conversion factors vary: The relationship between conductivity and hardness depends on the specific mix of ions in the water, which can differ from place to place.
However, we can make a reasonable estimate:
- General Guideline: A common approximation is that 1 µS/cm corresponds to roughly 0.5-0.7 mg/L of calcium carbonate (CaCO3), the standard unit for hardness.
- Applying it to Tin Win’s value: With a conductivity of 250 µS/cm, this gives us an estimated hardness of 125-175 mg/L CaCO3.
To put this in perspective:
- General Hardness Classifications:
- Soft: 0-60 mg/L CaCO3
- Moderately Hard: 61-120 mg/L CaCO3
- Hard: 121-180 mg/L CaCO3
- Very Hard: Over 180 mg/L CaCO3
Based on this, U tin Win’s 250 µS/cm water sample would likely be classified as hard.
With that said, it’s important to remember this is an approximation: For a more accurate measurement, you’d need a specific hardness test kit.
So, do CPD’s really prefer softer water? I’m not so sure anymore. At the very least, these fish are adaptable. If your water is at the higher end of the estimated range, you might consider measures to soften it slightly.