Splendor Koi: 2011

For those of us in the hobby cursed with an aggressively temperate climate (best defined as hot as Hades in the summer and cold as a well-digger’s-er-lunch in the winter), the need to protect the fragile and artificial environment of our ponds in cold weather is a major and recurring concern.

We need to be aware of several issues, all centered around water quality and the needs of our fish. Briefly, these are:

Pollutants, Temperature, Metabolism and pH. The goal is to try to maintain the same optimum conditions in the winter that we strive for with more ease during the ponding season. For those of us with unlimited money, the solution is simple. Build our house out around our pond, effectively moving the whole shebang indoors. Problem solved. Water stays at 75 degrees year round, filters stay active and if you dig the pond deep enough, you can go scuba diving with your fish any time you want. (Do not laugh. One of our local club members has done exactly that.) For the rest of us, we find ourselves up against a formidable opponent every year. Ma Nature does not like us or our works, even when we try to help her. We are forced to defend our small patches of artificial wilderness with all the wiliness at our disposal.
Pollutants: Our worst enemy. While colder temperatures slow down the ammonia production of our fish and send our filter bacteria into dormancy, it is important to remember that there are other processes in our ponds that have the potential to severely degrade the water quality under cold conditions and threaten the health of our fish. The enemy is sludge, the collection of broken down organic crud that lodges between and behind all those beautiful big rocks around the sides of your pond and beneath that natural-looking thick layer of river rock and gravel on the bottom. (Those of you out there with bare-liner bottomed ponds can ignore this next bit. I’m a little biased here, and the proprietors of a certain pond construction style will probably go ballistic.) Ponds are living things. A good portion of a pond’s ability to convert nitrite to nitrate lives in its oxygen-poor areas; behind and under rocks and in areas where water movement is slow .The bacteria grow, divide, work and die, and the dead bacterial biomass accumulates in the dark areas we do not see.These are also areas where debris tends to settle, become trapped and break down, also adding to the load of organic materials that will accumulate over a normal season. As the water cools down and we turn down (or off) our filters and pumps, the bacterial populations in these areas change, shifting to anaerobic species. The result is the continued breakdown of organics, but with no easy way of getting rid of the result, a heady mixture of dissolved proteins and the toxic gas hydrogen sulfide. While the process can be partially dealt with by keeping the water moving and ice-free, it will not solve the dissolved organics problem, with its negative impact on water quality. The easiest and simplest solution is cleanliness. Clean the pond out each fall, preferably while the water and air are still warm and the fish are at their peak of health. Get your koi into a temporary holding area, drain out and save as much of your water as you can, and use the rest to rinse and sump out as much of the season’s crud and goo as you can. Bare-liner ponds tend to be mostly self-cleaning, so a pump in the bottom of the pond drained down to a foot deep can provide all the pressure you need to get behind the rocks. A hose water rinse and pumpout, refill, dechlor, and you’re done. Folks with gravel bottoms have a much harder job, but it is doubly important that they do it. Proponents of gravel-bottom pond construction assert that their ponds do not accumulate sludge, but also offer to come and clean out these ponds on a twice-yearly basis. I sense a conflict here… There is a temptation to pressure wash the sides of a pond during this exercise, and I’m not a fan of this. The algae adhering to the walls and rocks is actually beneficial, providing a minor amount of filtration and also cushioning on the rocks. It is also a non-toxic winter food source. Insisting on a sterile, stripped pond wall every year is a great way to have “new-pond syndrome” in perpetuity. Get the sludge out, but be gentle!
Temperature: Koi are cold-water fish, and will tolerate temperatures down to about 38 degrees without too much trouble. What they can’t tolerate is sudden changes in their environment at those temperatures. Events such as the sudden entry of a load of snow dumped through an inadequately-supported weather cover, the sudden freeze-over during an unexpected cold snap (and the subsequent frantic hammering of the ponder on the ice in an attempt to break through), or the gradual build-up of noxious pollutants from a deferred, incomplete or forgotten cleanout can kill them outright, or stress them enough to cause fatalities in the spring when the parasites awaken before their immune systems. The most obvious (and most expensive) means of dealing with this problem, aside from bringing the pond indoors, is to heat the pond. Many experienced koi-keepers do this, and there are several pond-heater designs available that work well.The cost in natural gas, propane or electricity to run them is significant, however, and there are other ways to deal with the problem. Many ponders set up indoor facilities for their fish and shut their outdoor ponds down for the winter, disconnecting their pumps and draining their pipe runs to prevent expansion damage. It is a system that works well for smaller fish and smaller ponds, but when your fish mature, it becomes progressively more difficult to provide acceptable water quality in the tight conditions that temporary indoor vats impose. Leaving the fish in the pond year-round presents other challenges. In climate zones with mild winters, a floating heater can be sufficient to keep enough of the pond’s surface ice-free to get them through. The problem with these devices is that, for the most part, they are designed to keep horse troughs open enough to allow livestock to drink. They get overmatched in ponds. They also tend to corrode and short out, presenting another risk to the fish. Highflow airstones near the water’s surface are also possible, but can be overwhelmed by a really cold spell. The system we use, and which I wholeheartedly support, is to cover the pond. How you do it is up to you, but remember to take your local weather conditions into account. If your winters reliably present you with two feet of snow and subzero temperatures with winds approaching hurricane force, PVC pipe and a plastic tarp are not going to cut it. Our solution to Chicago winters was (and is) a $700 “hoop-house” kit purchased from a local landscaping supply business. A minor amount of modification created a structure that easily supports three feet of accumulated snow and, more important, keeps the wind off. We shove a small $15 electric radiator under the greenhouse-grade plastic and watch our perennials around the pond thrive. We have been ice-free for eight years.
Metabolism: This principle involves the whole pond, or just the fish. We tend to lose sight of two facts as we glide through the summer months: first, that our ponds are closed systems, and in the absence of a constant source of fresh water from “upstream” depend on a complex infrastructure to maintain water quality and fish health, and second, that everything in the pond environment is poikilothermic .This means that every living thing is dependent on the temperature of the water and will only function in temperature zones it is designed for. Koi digestive systems slow down and become incapable of digesting complex foods at about 50 degrees F. Their immune systems shut down at about 40. Thankfully, most parasites stop being active at or about 45. Unfortunately, so do our pond’s filtration support bacteria. It is essential to remember that while our fish may still be active and appear hungry as the water temperatures drop, the efficiency of our bioconverters is also dropping, right along with the temperature, and we need to be cutting back on the feeding. The Ponder’s Adage “A hungry fish is a healthy fish” was never more true than in the fall.
pH: Thought you were done with all that water testing, didn’t you? Not so fast, buckaroo! There’s still a little bit of water cleaning going on in the pond, even in the depths of winter. Ammonia is still being generated by the fish, algae is still growing, bacteria are still working, and consumable minerals (mostly carbonates) are still being used up. Alkalinity, the buffering capacity of your pond, (its ability to maintain a constant pH) is under constant, if slower, attack. Water changes are your friend here, pulling out about 5% of your pond’s volume from the deepest part of the pond and gradually replacing it with fresh (dechlorinated) will keep your alkalinity up and will help get rid of some of the dissolved organics too. Your pH will stay stable and your fish will thank you by being there in the spring. Look under that cover every day, test your water frequently, and dream of warmer times and climes.