Using Salt to Calculate Pond Volume

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Using Salt to Calculate Pond Volume

February 22, 2015 - 14:40

Yes, you can use the standard shapes above to calculate volume, but they are notoriously inaccurate.  Mike Anger, CKK,  teaches you a simple and ACCURATE way to calculate your pond's volume, after the break...  If you want to learn more, take K.O.I. Pond Construction #202 - CLICK HERE for more information about the course.

No matter what your pond interest, Koi, water plants, frogs, or just the peaceful sounds of a waterfall, there is one unifying factor: WATER. Temperature, pH, ammonia, nitrite and dissolved oxygen are key parameters to measure, water changes are important to perform, maintaining clarity to see your Koi and or plants is an ongoing task, and replacing water lost to evaporation (or leak) is a never ending chore. No matter what, knowing the actual volume of your pond is one of the most important facts to be aware of. Despite this, many of us are not too sure what it is, or to be honest have “exaggerated” its size. Ever visited a fellow club member’s pond and discussed the number of gallons? Have you looked at its size and compared it to your own? Sure you have. Sometimes it seemed strange that their 5000 gallon pond was much bigger than your 7500 one. Maybe it was the depth that was fooling you, or the dimensions were irregular. Maybe you thought that they were the ones stretching the truth (literally and figuratively.) In a survey done over a season by Duncan Griffiths (whose web site is an excellent information source) 85% of the ponds visited had stated volumes (by the owners) overestimated by 100%! Zero were underestimated-perhaps bigger is better is a sort of macho thing. This year, make a promise to yourself and try to get an accurate assessment of your own volume.

If you start with an empty pond, you can put a volume meter at the end of your water source (such as your hose) and record the amount it takes to fill. This is easily done when you first build a pond, though not so easily when filled with Koi that need to be housed while you do this. An alternative method requires calculations.

If a pond is a perfect rectangle with a flat bottom, vertical sides, no slope on the bottom and no rounded corners, the equation is: length times width times depth (all in feet) times 7.48 equals the total volume in gallons. For round ponds it is the radius times the radius times the depth (again all in feet) times 3.142 times 7.48. But what about an irregular shape? Several assumptions have to be made. If for example the bottom slopes from 3 feet at one end to 6 feet at the other, use an average of 4.5 feet. If the sides are sloped so that the width is 12 feet at the top and 10 feet at the bottom, you would use an average width of 11 feet. For more irregular shapes, you might need to break the pond into sections, calculate each one and add them together.

One of the problems with these estimates is that they don’t take into consideration the volumes in your filters. The way I suggest is to use salt to measure volume. Yes, you will have to remove the salt with water changes, but you'll be doing those anyway.  You can utilize salt in your pond to get a fairly accurate water volume. One pound of salt in twelve gallons of water equals 1% salinity; one pound in one hundred gallons of water raises the salinity 0.12%. We can utilize the formula: Pounds Salt times 12, then divide this by %salinity change = Gallons of Water. To do this accurately, you need a salinity meter. First, estimate the volume of your pond as I have discussed above. Measure the % salinity of the pond before adding any salt (call this S1).  Add one pound of salt for each 100 gallons of estimated pond volume (best done by dissolving the salt in a bucket of pond water and carefully distributing it around the pond) and allowing it to be well mixed (at least several hours, or better, waiting until the next day) and taking a second % salinity reading (call this S2). Determine the change of salinity, which is S2 minus S1. If your initial salt reading is zero, then just use S2. Multiply the pounds of salt you added by 12, and divide this by the %salinity change (divide by S2 minus S1). This result will be your pond volume in gallons. (I bet it’s less than you thought).

Record this volume and use it when you need to estimate water changes or calculate medication dosages. You’ll be glad you did!


!If you're not havin' FUN, you're not doin' it right