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What size water pump do I need for a reservoir that hold “x” number of gallons?

The size of your pump doesn’t depend on the size of your reservoir; rather it depends on how far you need to pump your water and how much water you need to pump.

You want to avoid overworking your pump, so in choosing the proper pump you will want to choose one with at least 20% more power than need. To find out your appropriate pump size you will need to determine how much water is necessary to fill your tray. If your tray is in the shape of a rectangle or square then you will need to apply the following formula to determine its volume:

Length (ft) x Width (ft) x Average Depth (ft) x 7.5 = ? US gallons

This will give you the total gallons that your tray can hold. It is a good idea to always get a pump that is at least 20% larger than necessary to avoid overworking it.

After you’ve determined your volume requirements you need to find out how far “up” the water needs to be lifted in order to reach the tray.

Simply measure the distance between your pump and the entry point in your tray; most systems will have a distance of under 3’. This vertical distance will have an adverse affect on the pump and this affect must be accounted for. In essence, the greater the vertical distance the water must travel, the stronger the pump needs to be. The following chart will show you how vertical distance affects the pumps. Note the loss of power of each pump as the vertical height increases.

Pump Size (GPH)

Height Lifted

1ft     3ft     5ft     7ft     9ft

120     120     70     40     x     x

170     170     130     70     x     x

205     205     170     120     40     x

300     300     250     200     160     110

500     500     350     280     200     150

700     700     520     350     280     200

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