How to Raise Healthy Goldfish and Kois

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By bellerose
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Our 10-year-old comet goldfish

Goldfish and kois are among the hardiest and longest-living fresh water aquarium fish. They are sociable and usually friendly to people and to each other (although they sometimes bully smaller fish and fish of other species). The main challenge with them is keeping tank water clean. Here's how to keep them healthy and happy.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

Goldfish and/or kois
Tank large enough for all fish in it (more on this later)
Filtered tap water (use a Brita or similar filter)
gravel for tank floor
Tank filters and pumps
Flake or granular goldfish/koi food

Step 1

AQUARIUM: Set up your fish tank first, but think about the fish you'll get at the same time. It's best to start with less-fancy goldfish (the slim orange comets are hardiest) and kois with shorter fins (although kois are very hardy). Fish should be at least about 2 1/2 to 3 1/2 inches long. Four or five fish is enough to start with. Plan on 2 gallons of water for each inch of fish. So if you get 4 three-inch fish, that's 12 inches total, meaning tank should be about 25 gallons. But fish grow pretty fast. Four 9-inch fish (not unusual) would need about 70 gallons.
Step 2

WATER: Fill tank to 4-6 inches from the top with FILTERED water (always filter water you put in tank). Boil gravel in tap water, cool, strain off water and line bottom of tank with gravel. Set up filters and pumps to make sure they work properly. Plain bubbler pumps work well and are easier to clean than more complicated filter systems. Clean them out whenever filters look dirty (this can be often). Clean filters and water are probably the most important thing you can provide for fish, though, and their health depends on them. Water temperature for goldfish and kois should be about 70 degrees plus or minus 5 degrees.
Step 3

FISH: Choose active fish that look healthy. Some goldfish are very sociable. It is easier to have friendly fish than fish that are afraid of you if you have to treat them for a health problem later. Kois are a bit shyer but also become friendly in time. Carry your new friends home carefully.
Step 4

FOOD: Place fishes' carrying bag in tank and open slowly to let them out so the water temperatures inside and outside the bag equalize. Give them some time to familiarize themselves with the tank and give them a very small amount of food. Feed fish at regular times (twice a day is good) in small amounts (a small pinch of food for each small fish), so they finish it in a minute or two. Old uneaten food dirties water, making it unsafe for fish. Small goldfish flakes and pellets are always good; stick with them at first.
Step 5

CLEANUP: Clean filters as often as you have to--whenever they are dirty. This is very important. It also helps to replace some water in the tank with new filtered water; this can be up to a quarter of the water in the tank at one time without disturbing fish. About once a month, take some of the gravel out and rinse it clean before straining off wash water and putting back. Algae (slimy stuff) that may grow on the wall of the tank can be removed with a clean sponge.