Many people ask how we go about calculating the overall gallons in any particular pond that we are contracted to install.
The formula below is commonly used in this industry to figure it out.
Length x Width x Average Depth x 7.48 = Total Gallons
For example, say you want to have an 11′ x 16′ pond installed at a standard 2′ depth.
Your formula would be: 11 x 16 x 2 x 7.48 = 2633 gallons
It has been our experience that this calculation is always high. I’m sure that it is perfectly accurate if you are building a rectangular box that is exactly 11′ x 16′ x 2′. But, you aren’t building a box, you’re building a pond. A pond has curves, rocks, shelves and plants, it would be impossible to determine exact water quantity using a formula. The formula gives us the wrong answer every time because your pond is not square or rectangular and it is not an average of two feet deep. It would probably be a closer guess to say that this example pond is 10′ x 15′ x 1.5′ which would equal 1683 gallons.
Not to Worry
From my experience this figure would be more accurate, but the only way to be sure is to use a water meter to fill your pond. I never worry about the accuracy of this formula because it gets us close enough for pump sizing and I never use chemical water treatments, so I don’t need to worry. It is never a problem to estimate a bit high, unless you are adding some sort of chemicals to your pond. If you are, watch out! An over dose of chemicals can kill plants, fish and frogs in a big hurry. We only recommend using natural bacteria and enzymes in your pond. The combination of these natural products and a good mix of plants and fish will keep your pond clean and clear without resorting to the killer chemicals. When using bacteria and enzymes, you can’t over dose, so you don’t need to worry.
Pump Sizing
The standard in the water garden industry is to suggest that a pond’s total gallons of water should be turned over once every hour. From my experience, this certainly works, but isn’t always necessary. As with most pond questions, the answer to this one is variable. Ponds are unique, each one has its own requirements that you and I could never figure out using a formula. I have found many ponds that do quite well with much less water flow than recommended. The once per hour rule is definitely a safe rule, but with time, you will learn what works for your pond. I have had clients who have cut their pump size in half with no adverse effects on water quality. The better constructed and balanced your pond is, the more forgiving it will be.
Fish Factor
If you have, or plan to have a heavy fish load in your pond, your more ideal target is going to be 1-1/2 – 2 times per hour to maintain beautiful water quality. The more fish that you have, the more filtration that you will need, the more plants that you will need and the more water flow that you will need.
In the case of the 11′ x 16′ pond example that we used, we would recommend a 3000 gph or more depending on the customers budget and desire for water movement and sound. Having said that, I have run my 11′ x 16′ pond (built in 2003) at home using a 1500 gph pump for the last two years and it works just fine, but it is well established and not over loaded with fish.
Not all Pumps are Created Equal!
Please keep in mind that usually you get what you pay for. Pump specifications vary greatly between manufacturers. I have found that the more solidly built professional style pumps will move a lot more water than any of the plastic cased, more economical pumps. These pumps are often sold as more energy-efficient, but by what measure? Sure they use less energy per hour, but they are also moving much less water per hour. Many factors affect a pump’s performance, make sure that you take some time and thoroughly research your pump choices before purchasing anything.
Should you have any difficulties with this formula, feel free to call us for assistance!