The standard for pond circulation is a complete exchange of the pond’s volume once per hour. This means a 500 gallon pond needs a pump rated for 500 gallons per hour. If you choose a pressurized filter system instead, you can downsize the pump by half and would only need a 200 GPH device for a 500 gallon pond. Check out pump prices and the wiring required for the devices before deciding the total volume of the pond. You may be surprised at the cost and decide to downscale your plans to save money on equipment for keeping water quality high enough for fish and plants.
Without adequate circulation each day, the pond water grows stagnant. This reduces dissolved oxygen, interferes with the natural water cleaning cycle, and allows waste products like nitrates to build up from fish waste. If your pond doesn’t contain any fish or plants, you may be able to get away with fewer circulations per day by a factor of half or more. However, this is only recommended if you don’t plan to swim in the water either. A pond with a low number of full volume circulations per day will be murkier and may have a stronger odor than one that has a healthy number of exchanges.
