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Water pumps and their practical function in the pond were not one of my strong points when I first built my pond.  Now, however, after going through several of them (they do wear out eventually), I consider myself something of a pump expert.  My original mistakes were not in the pump purchase, but were in the choices I made afterwards.  I had created dual waterfalls, and the plan was to divert the water evenly using a simple plastic T fixture. I bought a 1200 gallon per hour pump and the biggest tubing I could find in the water garden store.  That tubing was only about 1/2" and I had to buy all kinds of fittings to hook it up to this big pump.  I finally got done and turned it on, and it was a disappointing trickle down both spillways.  I lived with that for a while until a knowledgeable friend came by.  I complained about it and he straightened me out with these words, "Get a bigger pipe, stupid."  It was at that precise moment that I came to the realization that you don't have to buy all your water garden supplies in the water garden department.  The plumbing department yielded tubing in all kinds of big, roomy sizes.  I found one that fit my pump, hooked it on with a stainless steel adjustable automotive clamp, and poof -  two beautiful spillways with full water flow.

Your pump is going to be the heartbeat of your pond - it will move the water, provide critical aeration, and be the center of your filtration system.  If you have one or more waterfalls, you need to know how far a pump is going to have to push water uphill for it to spill back down the waterway appropriately.  Your pump will probably be a submersible one - most of them are these days because they are easy and efficient. 

Basically, the most important thing the pond owner needs to know is how many gallons per minute you will need to pump to push the correct amount of water, expressed as gpm (gallons per minute).  If you are going to use a decorative nozzle to shoot water up instead of a spillway, look on the nozzle package (there is a chart specific to that nozzle there) for specifics on what pump to get.

If you are building a waterfall, look at the spec sheets for pond pumps, and take note of the Head Rating chart.  The Head rating is basically how far the pump can push water straight up before the water can go no further.  This is the data you will need to choose the best pump for your purposes. 

For instance, for a Beckett Little Giant WG-65 pump, the chart looks like this:

Head (Feet) Flow (Gallons per hour)
1 1950
5 1650
10 1100
15 520
20 0

Therefore, at 1 foot, that pump will push near 1950 gallons of water per hour under perfect conditions.  There are some variables with each unique installation, however, including twists and turns in the piping going up the waterfall, which will decrease these values somewhat, and how far under the water the pump sits, which adds to the distance the water has to be pushed.   Also, as water travels upward through a pipe, some of it's force is lost, and this is called friction loss, which will also decrease these values.  So taking these variables into account, expect performance that is slightly less than shown on the chart, but in all but extreme cases such as a very tall waterfall, these charts are an adequate frame of reference for the average pond builder.

When choosing a pump for a waterfall, you obviously want one that gives the effect that you desire.  Do you just want a gentle drip or do you want a powerful flow?  Fountains will give you the recommended flow on the package, but if you are building a free-form waterfall, here's the formula:  For every inch of "sheet water," plan for 100 gph at whatever height your waterfall is.  For instance, using the chart above, if your drop is 5 feet, you would have a good sheet flow on a 16 1/2 inch wide spillway.  

Your pump will also be the center of your filtration system, so in addition to the above calculations, you will need to know the volume of your pond to find an adequate pump for your purposes.  Simply multiply the average width x average length x average depth of the pond to come up with the volume.  Then multiply by 7.48 to convert to gallons. 

For instance, a pond that is 10 feet long x 6 feet wide x 2 feet deep would have a total area of 120 square feet.  Multiply 120 x 7.48 to convert to gallons = 897.6 gallons.  If you have an irregular pond, just do the best you can by measuring averages for size and depth to get a number for the volume of the pond.  The point is to get a general idea of how many gallons you will have to filter per hour, and an exact figure is not really necessary.  For filtration purposes, more is always better, and you should never get a pump that doesn't turn at least half the water in the pond over per hour, which you will find is probably inadequate in the long run.  Your target should really be to turn over all or more than all the water in the pond per hour. Once you have done the calculations for the waterfall or fountain in addition to the filtration volume, you can make an educated decision on what pump to choose for your project. 



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