Common Pond Misconceptions
You need catfish to clean your pond. Catfish actually do little to clean a pond, koi and goldfish are actually better scavengers than most catfish. The typical catfish sold for ponds grow very big very fast and eat all of your little fish.
Snails help you control algae. An adult Trapdoor snail of the kind typically sold for ponds can keep an area about two square feet clean of algae. That means you need lots and lots of them to eat all of your algae. Most of what they eat is the thin film of algae that grows on your rocks and liner, which is actually very beneficial and you would be better off to keep it. Also, big koi (say, 12” and larger) find your snails to be a very tasty though expensive snack.
If you let your water sit overnight you don’t need to dechlorinate. This was true when cities actually used chlorine in the water. They don’t anymore. Now they all use chloramines, which take up to six weeks to break down on their own.
If you just add a little water, you don’t need to dechlorinate. We hear this one a lot and see it on the internet. “I’ve been adding water for years without dechlorinating and my fish are just fine”. Well, they aren’t. Adding just 5% or even 10% chlorinated water to your pond may not immediately kill your fish, but it burns their gills a little bit each time and it takes them months and months to heal from it. It is equivalent of making them smoke a couple of packs of cigarettes each day. It might not kill them immediately, but it sure affects their health and lifespan.
You need to move all of your plants to the bottom deepest part of the pond for the winter. Maybe if you live in Buffalo New York, but not here. Take out your floating plants at the first frost and toss them, then leave the rest of your plants right where they are for the winter.
You need to heat the pond in the winter or take your fish inside. Koi and goldfish both do not mind cold temperatures at all. You can even freeze them in a solid block of ice and they will be fine if allowed to thaw out naturally. The danger is if the entire surface freezes but the deeper parts of the pond don’t. Even dormant the fish are breathing very slowly and other organic processes are taking place. CO² builds up in the water and can’t release into the air and becomes toxic. Your pond needs a small ice free area, but doesn’t need the whole pond heated.
You need to clean your filter every week or every month. Cleaning your filter too often is counter productive. Completely cleaning a filter will kill all of the beneficial bacteria growing in it and it will take up to a month to fully re-establish itself and cycle, leaving your fish vulnerable to ammonia poisoning during that time and to particulate build-up.
You need to change 10%/15%/20% of your pond water every month. This one does have some small basis, but not much. A pond with no plants will build up nitrates and phosphates to annoying but not dangerous levels over time. Plants in a pond will take care of this for you. Water hardness will also build up for you over time, but it takes a long time in our area for it to become a problem. We would recommend a 50% water change once a year as sufficient to deal with these issues. If you have no plants and high phosphate you might want to do a change every six months, but not monthly.
You can’t mix koi and goldfish in a pond. Common as this belief is, it’s just plain silly. They are both just different species of fancy carp. They are fine together.
You can’t keep plants with koi. Anyone who has been here and looked at our display pond in the summer knows that this one is wrong. The trouble arises when you don’t have enough plants. One or two water lilies with twenty koi and the plants have no chance. You have to have enough plants that they can grow faster than the koi eat them. Lots of plants. I mean lots and lots of plants.
You need to clean the green slime off the sides and bottom of your pond. This one isn’t so much a misconception as a desire for some people. The answer is Don’t. The green slime growing on everything in your pond is highly beneficial to your ponds health. Called your biofilm or pond patina it is a collection of algae, bryozoans, bacteria and even microscopic crustaceans and is critical to the long term health of your pond.
If I have a pond, I’ll have a mosquito problem. Actually, with a pond you usually have fewer mosquitoes. Koi and goldfish will eat any mosquito larvae that show up in your pond, and ponds attract dragonflies. A dragonfly (known in much of the world as a mosquito hawk) will eat near it’s weight in mosquitoes daily. Your pond will also attract frogs and toads who will eat mosquitoes as fast as they can.
I can save on my electric bill with a timer to turn my pump off at night. Unfortunately, pond filtration depends on bacteria that needs constant water flow to stay alive. Four hours of no water flow and half of your bacteria has died, ten hours and 90% of it has died and it can take weeks to recover.
I can put gravel in the bottom of my pond for appearance. Gravel in the bottom of a pond traps fine debris which rots there creating issues with your water quality. Rocks on the bottom should be at least the size of eggs so you can get water flow between them and should be smooth rather than sharp so they don’t puncture your liner. You are perfectly fine putting nothing in the bottom.
Neighborhood cats will eat my fish. We have four cats at the shop. I have two at home. None have ever bothered the ponds. As a general rule, cats don’t like getting wet. They will drink out of the ponds and watch the fish, but that’s all. When someone comes in and says “My neighbor’s cat ate my fish” our reply is “No it didn’t. It was a possum or a racoon or a heron, but it was not your neighbor’s cat.”
I can’t have a pond, I have too many trees / I have too much sun. You can have a pond almost anywhere. If it’s in lots of shade, put a net up in the fall to keep most of the leaves out. If it’s in full sun, an ultraviolet light becomes even more important. We have pond plants for both full sun and for full shade, and many that will do both. Your fish won’t care.
Having a pond will greatly increase my water / electric bill. Fortunately for us, water in Hampton Roads is relatively inexpensive. You will only completely fill your pond once, then top it off as water evaporates. Our display pond is 3300 gallons and it costs a little over $10 for the water to fill it, and probably $30 to $40 over the course of the whole year to keep it filled. Our display pond costs about $60 in electric per month to run, but we have a lot going on with it. Our smaller goldfish pond runs about $20 a month to operate.
As long as my UV bulb comes on and glows blue, it’s working. Sorry, not true. UV bulbs have a useful life of about 9,000 to 10,000 hours. Note we said useful. UV bulbs are a type of fluorescent bulb and all fluorescent bulbs get dimmer as they age. After about 9,000 to 10,000 hours your bulb has dimmed enough that it is no longer strong enough to kill what it needs to. It may come on and glow blue for another two years or more, but after that first 10,000 hours, it’s just a very expensive nightlight.