Pumps and Skimmers [FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]You next have to estimate the volume of your pond in cubic feet using equations for the shape or by drawing top and side views of your pond to scale on graph paper and counting the squares. Each cubic foot equals 7.5 gallons of water so find out how many total gallons of water your pond will hold. Remember, you will need to keep the water level 10 inches from the top of the rocks, bricks or what ever material you have surrounding the edge of the pond to keep critters out and fish in the pond. Koi can jump higher than you think and many have jumped out of a pond when startled. Once you know the gallonage of your pond, then select a pump that will turn over that amount of gallons within 2 hours. Less time is better. So if you have a 4000 gallon pond, add 25% for the water in the rest of the system and filters for a total of 5000 gallons and select a pump that can pump at least 2500 gallons per hour or dividing by 60 minutes gives about 42 gallons per minute. [/FONT][/FONT]