Koi Ponds

Three feet is the minimum we will build for koi, four to five feet is what we recommend, and six is worth it on a large pond. Depth does three things: it stabilises water temperature through Los Angeles summers and the odd cold snap, it gives fish somewhere a wading heron cannot reach, and it gives koi the water column they need to develop proper body shape rather than staying stunted. Depth also has a code consequence here, since anything over eighteen inches is treated as a pool for barrier and permit purposes.

A koi pond is built for fish and a water garden is built for plants, and almost every specification follows from that. Koi ponds are three to five feet deep with a bottom drain, a settlement chamber, heavy biological filtration, high turnover, continuous aeration and relatively sparse planting, because koi eat and uproot plants. Water gardens are one to two feet deep, densely planted with lilies and marginals, lightly stocked with goldfish if anything, and filtered far more modestly because the plants do much of the work. Water gardens cost less and are more forgiving. Koi ponds cost more and keep large fish healthy for decades. Trying to run koi in a water garden is where most of the problems we get called about begin.

Plan on about 250 gallons per adult koi, and 500 per fish if you want large or show-grade specimens. A 2,000-gallon pond therefore comfortably holds around eight adult koi, not the twenty small ones it would appear to hold on the day they go in. The mistake almost everybody makes is stocking to the size of the fish at purchase: a 6-inch koi becomes a 24-inch koi, and the waste load grows with it. Overstocking shows up as ammonia spikes, persistent green water, stunted growth and disease. If you plan to add fish over time, size the filtration for the pond you will have in five years.

Sometimes, and it depends almost entirely on depth. If the pond is already three feet or more, adding filtration, aeration and a skimmer is straightforward and we do it regularly. If it is a typical two-foot garden pond, the honest answer is that the useful upgrade is a rebuild: a bottom drain has to sit at the lowest point under the liner, and retrofitting one means emptying the pond and re-lining it anyway. We assess the existing build, price both options and let you compare, rather than selling an upgrade that leaves the fundamental problem in place.

Pond-store koi run $20 to $75. Good-quality domestic and imported fish from a specialist dealer run a few hundred dollars each, and show-grade Japanese koi go into the thousands. Southern California is one of the better places in the country to buy, with several serious dealers within driving distance. Whatever you buy, quarantine it for two to four weeks in a separate tank with its own filtration before it joins the pond. Nearly every disease outbreak in an established pond arrives with a new fish, and the cost of a quarantine tank is trivial next to losing a stocked pond.

Design first: four feet of depth with steep sides means a heron cannot wade, and a fish cave, shelf overhang or length of wide pipe on the bottom gives the koi somewhere to go when a shadow passes. Raccoons work the shallow margins at night, so avoiding a gently shelving edge all the way round helps against them too. Beyond the build, netting through spring and autumn is the only complete answer, and a motion-activated sprinkler is surprisingly effective against both. Herons are common across Los Angeles along the river, Ballona Creek and the Sepulveda Basin, so this is not a hypothetical problem here.

Three stages, in order. Mechanical: a bottom drain feeding a settlement chamber or vortex, plus a surface skimmer, so solids leave the water before they break down. Biological: media with enough surface area and slow enough flow for bacteria to convert ammonia to nitrite and nitrite to nitrate, sized to the fish load rather than to the gallons. Ultraviolet: a correctly sized clarifier that kills suspended algae, which matters on a sunny Los Angeles pond with the light fish ponds get. On top of that, aeration running continuously and turnover of one to two pond volumes an hour. Skip the settlement stage and the biological media clogs; skip the aeration and the fish struggle in August.

Four to six weeks from filling, and the wait is not optional. A new filter has no bacteria in it, so ammonia from the first fish has nothing to convert it and levels climb until they are toxic. The pond is cycled by seeding beneficial bacteria and either running it fishless with an ammonia source or stocking a very small number of hardy fish and testing daily. When ammonia and nitrite both read zero and nitrate is climbing, the filter is working. Then stock gradually over a few months rather than all at once. Most new-pond fish losses in this city are a cycle that was rushed.