Koi Pond Filtration: The Complete System Guide
Drum filters, bead filters, UV clarifiers, bottom drains — everything you need to know about filtration for a SoCal koi pond.
Read Guide →Pump Calculator
Fill in your pond and waterfall. The result updates as you type. It uses the same method as our original pump calculator; the guide below explains each step.
Choose your water feature to start.
How this works
Sizing a pump comes down to two numbers: flow, in gallons per hour (GPH), and head, the resistance in feet the pump has to push against to deliver that flow. This guide walks through the method behind our pump calculator[1], then checks each step against manufacturer data.
Step 1: Flow (Gallons per Hour)
The calculator first asks what kind of water feature you have, then works out flow like this[1]:
| Water feature | Flow formula (GPH) |
|---|---|
| Pond with waterfall | pond gallons × 1 + spillway width (ft) × flow per foot |
| Pondless waterfall | spillway width (ft) × flow per foot |
| Pond with no waterfall | pond gallons × 1 |
Flow per foot of spillway, by the look you want: Trickle 700, Sheet 1,200, Heavy 2,500 GPH per foot[1].
Turnover. The "pond gallons × 1" term turns the whole pond over once an hour. Treat that as the minimum. For a koi pond, our filter guide recommends designing toward 1.5× pond volume per hour.
The waterfall flow is added on top of the turnover, not counted as part of it. The calculator adds the two together[1]. A 3 ft sheet waterfall on a 3,000-gallon pond needs its 3,600 GPH in addition to the pond's turnover.
How our waterfall figures compare with manufacturers'
Manufacturers usually quote waterfall flow per inch of spillway. Converted to per foot (× 12):
| Waterfall look | Our calculator[1] | Common per-inch rule | Laguna (Hagen) 2010 catalog[2] |
|---|---|---|---|
| Trickle | 700 GPH/ft | 50 GPH/in → 600 GPH/ft | — |
| Sheet | 1,200 GPH/ft | 100 GPH/in → 1,200 GPH/ft | 75–100 GPH/in → 900–1,200 GPH/ft (one range, no look named) |
| Heavy | 2,500 GPH/ft | 200 GPH/in → 2,400 GPH/ft | — |
The sheet figure matches the common rule exactly. Our trickle and heavy figures run 100 GPH per foot higher. Laguna's single range tops out at our sheet figure. Laguna measures the width "at top of Waterfall"[2].
Step 2: Head (How Hard the Pump Has to Push)
Head is measured in feet. The calculator estimates it as[1]:
Head (ft) = tubing length (ft) × 0.1 + head height (ft) + 10 if you have a pressurized filter
- Head height is the vertical lift. Measure from the pond's water surface to the top of the waterfall, not from the bottom of the pond[2].
- Pressurized filter. The calculator's note reads: "Pressurized filter systems like Aqua Ultraviolet Ultima II filters will add head pressure back on the pump"[1]. It adds the 10 ft only if you answer "Yes". Choosing "I Don't Know" adds nothing[1], so check what you have.
- Pond with no waterfall. The calculator doesn't ask for a head height in this case, so head comes from tubing length (plus the filter allowance)[1].
Is 0.1 ft of head per foot of pipe right?
Sometimes. Laguna's catalog uses the same rule: "Add 1 foot of head height for every 10 feet of hosing"[2]. A much steeper rule you may also see: add 10 inches for every foot of tubing, which is about 0.83 ft per foot, or more than eight times as much.
In reality, friction depends on how much water you push and how wide the pipe is. PerformancePro's friction-loss chart for Schedule 40 PVC (feet of head lost per 100 ft of pipe) shows how much this varies[3]:
| Flow | 1½" | 2" | 2½" | 3" |
|---|---|---|---|---|
| 50 GPM (3,000 GPH) | 14.25 | 4.16 | 1.75 | 0.60 |
| 100 GPM (6,000 GPH) | not listed | 15.03 | 6.33 | 2.18 |
The calculator's rule works out to 10 ft per 100 ft. That is about right for 2" pipe at 80 GPM (4,800 GPH), where the chart shows 9.94 ft[3]. It is too low when the pipe is undersized for the flow, and too high when the pipe is generous. Engineering ToolBox's Schedule 40 table gives the same picture (for example, 15.0 ft per 100 ft for 2" pipe at 100 GPM)[4].
These are figures for straight pipe. Bends and in-line equipment cost more. Excessive bending or the addition of in-line filters will reduce the flow.
Step 3: Read the Pump Curve at Your Head
The calculator's result reads: "We recommend a pump that gives you [X] gallons at a head height pressure of [Y]"[1]. The number that matters is the pump's flow at your head, not the big number on the box. As our filter guide explains, box ratings are measured at zero head, and real flow drops as head, pipe length and fittings add up.
Laguna's catalog puts it this way: find the column for your total head height, move across until the flow equals or beats your total GPH, and "This is the minimum size pump needed"[2]. Likewise, check the pump's packaging chart for the flow at different lifts.
Worked Example
Take a 3,000-gallon pond with a 3 ft wide sheet waterfall, 4 ft of vertical lift, 50 ft of tubing and a pressurized filter.
Calculator (1× turnover, the minimum)[1]:
- Flow: 3,000 × 1 + 3 × 1,200 = 6,600 GPH
- Head: 50 × 0.1 + 4 + 10 = 5 + 4 + 10 = 19 ft
- Result: a pump that delivers 6,600 GPH at 19 ft on its curve.
Same pond at the 1.5× koi target:
- Flow: 4,500 + 3,600 = 8,100 GPH, read at the same 19 ft.
- The calculator's head formula doesn't change with flow, but real friction does (see the table above).
Checking the pipe. 6,600 GPH is 110 GPM. In 2" Schedule 40, friction at 100 GPM is 15.03 ft per 100 ft[3], so 50 ft of pipe costs about 7.5 ft. That is already more than the calculator's 5 ft, and 110 GPM is a bit higher again. In 3" pipe, the same 50 ft at 100 GPM costs about 1.1 ft[3].
Engineering ToolBox also advises that velocities "should not exceed 5 feet per second." At 100 GPM, 2" Schedule 40 runs 9.8 ft/s and 3" runs 4.4 ft/s[4]. At 125 GPM, 3" pipe is already at 5.5 ft/s[4]. So 8,100 GPH (135 GPM) through a single 3" line would go over that guideline. You would need a larger line, or to split the flow between more than one return.
Submersible vs. External Pumps
Submersible pumps sit in the water, in the pond, a skimmer or a pump vault. Laguna describes its pumps as "completely submersible and designed to run continuously"[2]. Pondless waterfalls use one inside a pump vault (see our pondless waterfall guide).
External pumps sit dry, beside the pond. PerformancePro describes its self-priming Artesian2 series as "Excellent for applications positioned above the water level"[3]. The manufacturer also says its external design "helps protect your investment from potentially dangerous oil leaks and electrical hazards"[3]. That is the manufacturer's own claim.
Don't assume either type is more efficient. Compare the watts each candidate draws at your flow and head, using each pump's data sheet.
Energy Use: Why Watts Matter in Southern California
A koi pond pump normally runs around the clock, because it is what keeps water moving through the filter. That makes running cost a big part of the choice.
California's average residential electricity price was 33.61¢ per kWh in July 2026, against 18.31¢ for the U.S. as a whole (EIA)[5]. At that average:
- Every 100 W of continuous draw is 876 kWh a year, about $294 a year.
- A pump drawing 300 W around the clock costs about $883 a year. At 600 W, it is about $1,767.
These are illustrative figures. Your actual cost depends on your utility's tiers and time-of-use rates.
Variable-speed pumps let you run only as fast as you need. In PerformancePro's published data for the Artesian2 1.6 High Flow Variable[3]:
| Speed | Max flow | Current |
|---|---|---|
| 3,450 RPM | 160 GPM | 11.80 A |
| 2,600 RPM | 120 GPM | 5.20 A |
| 1,800 RPM | 79 GPM | 1.80 A |
Running at about half the maximum flow, the pump draws about 15% of the current. (Current is a stand-in for watts here, not an exact measure.) Turning a pump down when you don't need full flow can save a lot over a year.
Common Sizing Mistakes
- Buying on the box number. It is a zero-head figure. Read the curve at your head.
- Forgetting the pressurized filter. The calculator allows 10 ft of head for one[1].
- Undersized pipe. Friction climbs steeply with flow in small pipe[3][4].
- Too much pump for the waterfall. Water can gush over the sides instead of out of the spillway.
- Ignoring bends and in-line equipment.
- Counting the waterfall as turnover. Waterfall flow goes on top of pond turnover.
Related Calculations: Pond Volume
Pump sizing starts with your pond's volume. Our calculator measures in inches and divides cubic inches by 231[1], because one U.S. gallon is 231 cubic inches[6]:
- Round: π × radius² × depth ÷ 231
- Rectangular: length × width × depth ÷ 231
- Triangular: ½ × base × height × depth ÷ 231
Example: a 10 ft × 6 ft × 3 ft rectangle is 120 × 72 × 36 = 311,040 cubic inches, ÷ 231 = about 1,346 gallons. One cubic foot is 7.48 gallons[6], which is why some guides multiply cubic feet by 7.5[2].
FAQ
What size pump do I need for a 3,000-gallon koi pond?
With no waterfall, the calculator's minimum is 3,000 GPH at your head[1]. For koi, design toward 4,500 GPH (1.5×). Add any waterfall flow on top.
Can a pump be too big?
Yes. An oversized waterfall pump can push water over the sides of the spillway, and every extra watt runs all day. A variable-speed pump lets you turn the flow down[3].
Does pipe size really matter?
Yes, a lot. At 6,000 GPH, 2" PVC loses about seven times as much head per foot as 3" PVC[3].
Is the waterfall flow part of the turnover?
No. Size the pond turnover first, then add the waterfall flow[1].
Submersible or external?
Both work. Compare the watts each draws at your flow and head.
Sources
- Laguna Koi, Calculators page (pump calculator; WPForms form 17563 field labels and formulas; volume calculator form 17504). lagunakoi.com
- Rolf C. Hagen Inc., Laguna 2010 Water Gardening Catalog, "Choosing the Right Pump in 3 Easy Steps." Manufacturer catalog.
- PerformancePro Pumps, Product Catalog (Artesian2 series pages, Dial-A-Flow variable-speed curves, Friction Loss Chart). Manufacturer catalog. performancepropumps.com
- Engineering ToolBox, "PVC Pipes Schedule 40 – Friction Loss vs. Water Flow." Engineering reference. engineeringtoolbox.com
- U.S. Energy Information Administration, Electric Power Monthly, Table 5.6.A, "Average Price of Electricity to Ultimate Customers by End-Use Sector, by State, July 2026 and 2025." eia.gov
- NIST Handbook 44 (2026), Appendix C, "General Tables of Units of Measurement." nist.gov
All accessed 2026-10-03.