Aquarium Fish for Outdoor Fountains and Ponds

Ideal Conditions and Fish Species for Your Outdoor Pond

Garden pond with Koi fish

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Did you know that many common aquarium fish do not have to be kept in heated tanks under totally controlled environments? What if you could liven up that backyard pond or fountain with colorful tropical fish this summer? In certain environments, you can keep many aquarium fish outside year-round.

Benefits of Outdoor Fish Ponds and Fountains

Having colorful and active fish in fountains and ponds both outdoors and on porches can solve several problems you may otherwise have with outdoor bodies of water.

Any insect larvae that happen to be born in the water are prime food for the fish. The fish will find many healthy supplements to the prepared diets you feed them from the algae and other naturally growing outdoor goodies. You also will not have a cloudy water problem once you reach homeostasis.

Your fountain or pond will take on a level of interest for guests to marvel at, rather than just be a body of empty water.

Ideal Conditions for an Outdoor Aquarium

Many native tropical fish of temperate and sub-tropical climates can be kept and will thrive and breed in outdoor fountains and ponds if certain conditions are met:

  1. The average water temperature must be consistently over 65 degrees F at night and over 72 F in the daytime. When the weather starts getting cooler, the fish need to be brought indoors.
  2. The pond needs to be at least partially submerged in the earth, which “normalizes” the average temperature within the body of water. A fountain with a substantial wall thickness in the pond portion also could work. It should be of a size large enough that the summer sun doesn't overheat the water.
  3. The pond needs sufficient plants so the fish can seek shade from the intense summer sun, and the water level has to be kept up with either rainwater or aged water, not directly from a garden hose unless a dechlorinator is added to the water, though overspray from a sprinkler system will not hurt them in small amounts.
  4. Grass clippings should not be allowed to fall into the pond since this risks cross-contamination by pest control substances or fertilizers that could poison the fish and plants in the pond. Cut grass, leaves or other debris will also decompose quickly and contaminate the water, making it cloudy and increasing the ammonia level.
  5. Feed the fish once a day with commercial fish food, similar to what you would feed them in an aquarium.

Best Fish for Outdoor Aquariums

As long as tropical fish are put outside in ponds and fountains of sufficient depth after all fears of frost are over and brought back inside early in autumn before temperatures drop below 65 F, many species can thrive in the summer ponds of temperate and subtropical climates.

Some of the oldest varieties of aquarium fish are called tropical fish, but come from more temperate climates, and survive very nicely in unheated aquariums. The Paradise Fish (Macropodus opercularis) and the Whitecloud Mountain Minnow (Tanichthys albonubes) are good examples of hardy species of tropical fish that do not need much warmth.

Goldfish and Koi have long been good pond fish since they can even handle the water icing over the top of the pond in the winter. They must be protected from predators like cats and birds, and should be kept in deeper water than smaller fish. Goldfish and Koi are not effective in controlling mosquitoes like guppies and produce more wastes, requiring much more maintenance and filtration than smaller aquarium fish.

Guppy, Molly, Swordtail, White Cloud Mountain Minnow, Blue Gourami, Paradise Fish, Cory Catfish, and Plecostomus all are ideal for your outside pond project, as long as the water is aerated and filtered, and the water temperature doesn't get too hot or cold.

White cloud mountain minnow (Tanichthys albonubes)
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Acclimating Fish to Pond Water

Naturally, all fish must be properly acclimated to the outside pond water. 

If the pond is long established in homeostasis, it is a good idea to make a bucket of 1/2 pond water and 1/2 aquarium water and let the fish get used to the “natural” outdoor water for an hour, using an air stone and air pump to aerate the water. 

Whether or not you do this acclimation, you must put any fish in a plastic bag of the water they are coming from and float it in the pond to equalize the temperature for at least 15 to 20 minutes before releasing the fish into the pond or fountain.

Prepare for Outdoor Predators

Although most of the fish described above are hardy, you must look out for predators. Larger fish like goldfish and koi may be attacked by cats, racoons, herons or even passing birds of prey. 

The live bearing aquarium fish like guppies, platys, swordtails, and mollies are so prolific, however, that their constant addition of new fry will outpace just about any predator—another great reason to try these mosquito-eating marvels.

Keeping outside summer ponds free of mosquito larva also means no harmful chemicals are needed like chlorine and other pond and fountain maintenance chemicals.The pond should have a filter to remove the fish wastes, and periodic water changes should be made to keep the nitrate down, just like you would in an aquarium. Be sure to use a dechlorinator in the replacement tap water. If algae becomes a problem, causing green water, an Ultraviolet (UV) Filter can be used to keep the water clear.