I have one about that size, believe its 50 or 60 gallons
You could try the old 5g bucket method. Time how long it takes to fill a 5g bucket then time and fill the pond and do the math. It's not 100% but it is a great estimate.
You could try the old 5g bucket method. Time how long it takes to fill a 5g bucket then time and fill the pond and do the math. It's not 100% but it is a great estimate.