We have a 1800-2000 gallon pond with 4 koi. We have two pumps running to a biological filter and want to replace the two pumps with one big one and also add a UV filter. We came across a calculation for figuring out how much a pump puts out per hour but cannot seem to find it now. We want to figure out what the equivelant of the two small pumps would be to give us a better idea on what size should be for the one big one. The calculation we saw was to fill a five gallon container and to time how long it takes. One pump took 45 seconds and the other took 1 minute. The two together took 27 seconds. Do you know of this calculation or a different one?

One other question is, we have well water and the "general hardness" is
extremely high. What are your thoughts on lowering the hardness to an acceptable level.

Hi Craig,

Pump #1 is easy. 5gal/1min x 60min/hr = 300gal/hr

Pump#2: 5gal/0.75min x 60min/hr = 400gal/hr

Doing the same math with your combined flows gets you roughly the same number (actually a little less: 667
gal/hr)

Either way, it is inaccurate, because it does not take into account how high you are pumping this water to get to your falls, how long your pipe run is, how many elbows you have in the run or the diameter of pipe you are using. Each one of these parameters adds friction and reduces flow.

In any case, you are severely under-pumped right out of the box. The goal in biofiltration is to present each molecule of water in your system to your biofiltration media at least once an hour. For optimum bioconversion, your pond needs a pump that can deliver 2000gal/hour from your pump inlet to your falls, measured at the top of your falls.

Most good pumps come with a graph indicating flow loss per foot of "head" (how many feet above water level you are lifting the water) I'm sending along a series of tables that will help you estimate how much estimated "pressure head" you need to add to this number to calculate what any prospective pump you are thinking of buying will actually deliver to your falls.

Remember that your filters will also add resistance, especially if it is one of those commercially produced canisters with teeny-tiny inlet and outlet ports. It is actually a great idea to maintain the same pipe diameter throughout your system, and many advanced hobbyists actually increase the diameter of their pipe runs as they get further from their pumps.

The only problem that hardness will give you is a tendency for your kohakus to develop little black dots (called "shimmies") and your kawarimonos to go black in your water. This isn't dangerous to koi health, only dissapointing to the ardent hobbyist who just went to Japan and brought back a $10,000 fish which is now speckly and will *not* win Grand Champion. Don't worry about it, and don't get seduced into adding chemicals or hooking up a water softener (which only adds salt) to try to change it. That way lies madness.

(Answer courtesy Bob Passovoy)