One of the things I like most about koi is just how hardy they are. One of the things I like least about koi is just how hardy they aren't.
Sound like a contradiction? Not quite. I've been keeping koi for a little more than a decade now, and I've lost my share of them--at least I did in the early going. And then I learned a few things that have kept my koi swimming happily and healthily ever since. In fact, I'm convinced that, if you lose more than one koi a decade, you're doing something wrong, as this fella is:
1. I keep my koi in a still, shallow pond. After all, they're descended from carp, aren't they? They'll survive!
Fact. It's true that koi can withstand more oxygen-starved water than many breeds of fish, but that doesn't mean it's good for them. For the healthiest koi, buy a quality pump and keep the water moving! And you might add a filter, while you're at it.
2. Filter-schmilter. I just bought a pump. Why do I need to spend more money?
Fact. You don't, if you don't mind exposing your fish to a constant barrage of waste, contaminants, and potentially harmful chemicals. A mechanical/biological filter will remove the particulates that tend to congregate in the water. As a bonus, the water will be cleaner.
3. My koi are too small. I'm going to start feeding them more so they'll grow faster.
Fact. Actually, you can feed your koi as much as they'll eat, and they'll eat exactly as much as they need to grow absolutely as fast as they possibly can. Over-feeding isn't a problem--it's the increase in waste products that counts. Ammonia, nitrites, and nitrates are all potentially deadly to fish. If you're going to feed your koi heavily, you should plant as many water plants as possible to absorb the waste and give off oxygen in return). Add a biological filter to your mechanical filter for detoxifying harmful chemicals, and perform a partial water change at least monthly.
4. I don't need to make water changes, because where I live, I get half an inch of evaporation a day. I just top the water off, and I'm good to go.
Fact. You're a prime candidate for water changes. When pond water evaporates, it leaves a concentration of harmful chemicals behind to continue their nasty work. By draining a third of your pond's water and replacing it with pure, clean H2O, you're also removing a third of the accumulated chemicals.
5. My koi pond has a greenish cast to it, but the fish don't seem to mind.
Fact. They'll mind plenty when that accumulated algae--those one-celled animals that flourish in water and sun--begin using up all the oxygen. Do yourself and your koi a favor by using a fish-safe algaecide to kill off the suspended algae, which your filter will then remove. Or use my favorite: an ultraviolet filter. The UV rays from the light kill off harmful suspended algae, as well as potentially life-threatening bacteria, fungus, and parasites, producing a cleaner, happier koi colony.
6. I put my pond in the sunniest part of the garden so it really stands out.
Fact. Your pond may stand out, but you're not doing your fish any favors. Besides increasing algae blooms, sun can scald a fish's delicate skin, resulting in a host of problems. As an alternative, have some of your pond in sunlight and the rest in shade produced by trees, shrubs, rocks, arbors, or whatever else that does the trick.
7. I don't have a big, deep pond, but my koi don't seem to mind. In fact, they're even more active than some of the koi in my friends' larger ponds.
Fact. Koi need water at least 2 - 3 feet deep to provide them with a cool spot to hang out in summer and a warm spot in winter. It also tends to discourage predators, such as raccoons, wandering dogs, and carnivorous birds, all of which have been known to make a feast of a koi pond.
8. I feed the plants around my pond heavily to keep them lush and green.
Fact. If you're feeding your plants with commercial fertilizer, some of the nitrates and nitrites used in most plant foods is leaching into your pond. And that's not good for your fish. If you have to feed your plants, make sure you use a weak solution free of such chemical additives for the best of both worlds.
9. My friends feed their koi costly specialty food. I find they like goldfish flakes that I get at a discount store just as well. And I save a ton in food costs.
Fact. Inexpensive fish food is high in carbohydrates and low in protein and other beneficial nutrients. Any fish that grows as fast and as large as a koi does (some reach the size of small salmon) and lives for 70 - 80 years requires the finest food possible. Anything less will result in weakened fish susceptible to a wide range of diseases, parasites, and fungal infestations.
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