So you are designing an aquaponics system but how do you figure out what pump size to use?
There are some simple minimum rules of thumb that can help. For media bed aquaponics design it is generally recommended to pump at least the volume of your fish tank each hour (and I usually pump more than that in my systems.)
So the first step in choosing a pump size is knowing your fish tank volume. Say you have a 300 gallon fish tank so you know you want to move at least 300 gallons per hour.
Then you will also need to know how high you need to lift the water. A pump that is called a 300 gph pump will generally move far less than that if you ask it to be lifted at all. So measure from the surface of the water where the pump will be situated (if the pump is in a sump tank that will fluctuate in the extreme, then you can simply measure from the low water level at the pump intake) up to the highest point to which the pump needs to lift the water which will often be either just above the rim of the grow beds or the fish tank depending on the system design.
For example say you are lifting the water 3 feet.
Now it’s time to go looking for pump curves as these are very important in figuring out pump size. All good pumps should tell you how much water they will pump at different heights, if they won’t share that information, don’t buy the pump.
So by doing a little math one can figure out that the QP14 will move 600 gallons of water an hour at 5′ of head. So if the pump was going to run 30 minutes out of each hour, then this pump would be adequate to handle our 300 gallon fish tank example at 3′ head. If the pump was going to run constantly then the QP13 would be adequate to our example system. Notice that I tend to allow for some extra capacity on the pump since there will also be some pipe friction to overcome.
If for our Aquaponics example the pump is planned to run only 15 minutes each hour, then we need a pump that will move 4*300 per hour at 3′ head or 20 gallons per minute. The only choice left on this pump curve would be the QP17.
My 300 gallon Aquaponics system runs with a repeat cycle timer that has the pump on for 9 minutes then off for one minute and I’m lifting the water about 30 inches. So I’m pumping for 50 minutes per hour and I’m using the QP14 so I’m probably pumping almost 600 gallons per hour for that system and this seems like a fine thing to me.
If you choose an energy efficient pump then pumping extra water will only cost a little extra in electricity and may save you quite a bit in keeping your water quality nice.