Pond and water feature glossary
Plain-English definitions of the pond and water feature terms homeowners meet on a quote: skimmer, bog filter, bottom drain, head height, KH, turnover rate, pondless waterfall, and more.
A
- Aeration
- Adding oxygen to pond water, usually with an air pump and diffuser stone or by moving water over rock. Warm water holds less oxygen, so aeration matters most on still summer nights. Pumps and running cost
- Algae bloom
- A sudden growth of single-celled algae that turns pond water pea-green. It is a symptom of excess nutrients and light, not a disease, and clears when the underlying nutrient load is fixed. Algae causes and real fixes
- Ammonia (NH3)
- The waste product fish excrete and the first number to test in a new pond. Any reading above zero is a problem; beneficial bacteria in the filter convert it to nitrite, then nitrate. The five water-quality numbers
B
- Beneficial bacteria
- The nitrifying colonies that live on filter media and rock surfaces and convert fish waste into far less toxic compounds. They take four to eight weeks to establish in a new pond.
- Biological filter
- The chamber that houses beneficial bacteria on high-surface-area media. It removes dissolved waste rather than visible debris, and should never be cleaned with tap water.
- Bog filter
- A gravel bed planted with marginal plants that water is pushed up through. It works as both a biological filter and a nutrient sink, and is one of the quietest, lowest-maintenance ways to keep water clear.
- Bottom drain
- A gravity drain set at the lowest point of a koi pond that pulls settled solids out continuously. It is the single biggest difference between a koi pond and an ornamental pond. Koi pond water quality
C
- Check valve
- A one-way valve on a pump line that stops water siphoning backwards when the pump shuts off. Without one, a waterfall can drain part of the pond every time the power cuts.
D
- Dissolved oxygen (DO)
- The amount of oxygen available to fish and bacteria, measured in mg/L. Koi are comfortable above about 6 mg/L; distress is usually visible at the surface before a test kit confirms it.
E
- Edge treatment
- How the liner is hidden and the water meets the garden — cobble beach, boulder shelf, planted margin, or stone coping. Edge treatment is what separates a pond that looks built from one that looks found.
- Evaporation loss
- Normal water loss from surface area and moving water. On the Central Coast a modest pond typically loses roughly an inch a week in summer; anything faster suggests a leak. Finding a pond leak
F
- Flow rate
- How much water a pump moves, in gallons per hour. A general pond target is turning the full volume over once an hour; a koi pond usually wants more.
H
- Head height
- The vertical distance a pump must lift water, plus friction losses in the pipe. Pump output falls as head height rises, which is why a pump rated 5,000 GPH may deliver half that at the top of a waterfall.
K
- KH (carbonate hardness)
- The water's buffering capacity — its ability to resist pH swings. Low KH is the usual cause of overnight pH crashes in a young pond. The five water-quality numbers
L
- Liner
- The waterproof membrane that holds the pond, usually 45-mil EPDM rubber over a protective underlay. Quality matters less than protecting it properly from roots and sharp rock.
M
- Marginal plants
- Plants that grow with their crown at or just below water level on a planting shelf — rush, sedge, iris, pickerel weed. They soften the edge and consume nutrients algae would otherwise use.
N
- Nitrate (NO3)
- The end product of the nitrogen cycle. It is far less toxic than ammonia or nitrite, but high levels feed algae, which is why plants and partial water changes still matter.
- Nitrite (NO2)
- The intermediate stage between ammonia and nitrate, and dangerous to fish at low concentrations. A nitrite reading above zero means the filter has not fully cycled.
O
- Overflow
- A deliberate outlet that carries excess water away during heavy rain. On Central Coast sites with winter storms, an overflow routed to a drain or swale is what keeps a pond from flooding a patio. Same-day storm checklist
P
- pH
- How acidic or alkaline the water is. Koi are content between roughly 7.0 and 8.5; stability matters far more than hitting an exact number.
- Pondless waterfall
- A waterfall and stream that disappear into a gravel-filled basin instead of an open pool. No standing water means no fish, less maintenance, and fewer safety concerns with small children. Pondless waterfall pricing
- Pump vault
- A buried, accessible housing that holds the pump in a pondless system or reservoir. Access matters — a pump you cannot reach is a pump that will not be serviced.
S
- Settlement chamber
- A vessel between the bottom drain and the filter where heavy solids drop out of suspension before the water reaches the biological media. It keeps the filter working and makes cleaning quick.
- Skimmer
- A wall-mounted or floating unit that pulls surface water across a weir and traps leaves in a basket before they sink. In an oak-shaded Santa Cruz garden it does more for water clarity than any chemical. The maintenance schedule
- Spillway
- The stone or manufactured lip that shapes the falling water. A slightly undercut, level spillway gives a clean sheet of water; an uneven one dribbles down the rock face.
- Stream bed
- The shaped channel a stream runs down, lined and set with gravel and boulders. Sound comes from the drops, not the length — a well-built six-foot stream can be louder than a flat twenty-foot one.
T
- Turnover rate
- How often the entire pond volume passes through the filtration system. Once per hour is the usual ornamental pond target; koi ponds are often designed around twice.
U
- UV clarifier
- A lamp in the plumbing line that kills suspended algae as water passes. It clears green water reliably, but it treats the symptom — nutrient control is the cure. Algae causes and real fixes
W
- Water garden
- A pond designed around plants rather than fish, typically shallower and heavily planted with lilies and marginals. Easier to keep clear, and a good fit for smaller gardens.
- Waterfall weir
- The manufactured box at the top of a waterfall that spreads pumped water evenly across the spillway and often houses biological media.
- Winterizing
- Preparing a pond for the cold season — stopping feeding as water cools, netting leaves, clearing debris, and checking overflow. On the Central Coast it is about rain and leaf load far more than ice. Winterizing a coastal pond
Keep going
Every term here is covered in more depth somewhere in the library.