iam thinking of building a pond and iam looking a filters and what is the normally watts for a 2000 litres to 3000 litre filter, try to work on elctric cost.
It just depends on the pump you choose. Typically external are more efficient than submersible. The manufactures ratings are often about 2/3 of the actual power consumed if you actually test the pump yourself. Depending on the pump you choose probably 75-200w.