What kind of pond? Concrete, liner, plastic,.......
How many gallons, kind of filter, and algae growth?
Sounds like you already understand that your liner pond is lacking minerals. Concrete ponds don't have this problem.
This being a new pond, there may be other factors and perhaps it is just not cycled yet.
sea shells can help with hardness, also don't mollies like a bit of aquarium salt added to the water ? Or is that an old thing