How Does Light Affect Goldfish?

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Goldfish need light to maintain good health, preferably a full-spectrum aquarium light to emulate their natural environment, helping them to keep their vibrant color, make vitamin D, and know when to eat. Goldfish do not have eyelids, so they depend on their environment to tell them when it's time to be awake, time to eat, and time to sleep. So, in addition to adequate amounts of the right kind of light, goldfish also need darkness — about 12 hours of each daily to mimic day and night.

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Goldfish need light to maintain good health.

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Imitate life in a pond

A goldfish's natural environment is a fresh-water pond or lake where the sun comes up and goes down in a regular daily pattern. Goldfish are most active during the day, swimming, eating, and exploring their surroundings. When darkness falls, they become less active, stop eating, and go to sleep.

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When you recreate this day/night pattern in their aquarium, it helps regulate their sleep cycle, which is necessary for good health. Many aquarium owners install a timer on the light so they don't need to be concerned if they are not home to turn the light on and off or if they forget.

Benefits of full-spectrum aquarium light

When it comes to lighting your goldfish tank, full-spectrum aquarium light bulbs are an ideal all-around type of light for a goldfish tank. Full spectrum means they emit all the colors of the color spectrum, so they are like real daylight conditions.

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Other types of lights are good for certain purposes. Blue light can highlight a goldfish's color, and both blue and red light help aquarium plants grow. Full-spectrum aquarium light contains red and blue, and the plants will pick them up. If you use a one-color bulb continuously instead of a full-spectrum bulb, it will create an unnatural environment for your goldfish.

Consider aquarium plants' needs

If you only want to have a plastic plant or two in your aquarium, you don't have to worry about what they need to flourish, but if you want to imitate a goldfish's natural environment accurately, choose live plants that are aesthetically pleasing but easy to grow. You can decide whether to grow varieties that goldfish like to nibble, such as vallisneria; plants that goldfish will leave alone, like marimo moss balls; or both. Either way, live plants help keep a stable level of oxygen and clean the water.

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Simulating daylight and darkness is good for the goldfish but also helps the plants go through photosynthesis using the light energy to exchange oxygen, carbon dioxide, and water vapor. Goldfish also like to sleep near plants and dig around them, so be sure that any you grow are properly anchored.

Providing darkness curbs algae growth

Having 12 hours of darkness each day not only helps your goldfish keep to a healthy wake/sleep regimen but it also helps cut back on algae growth in the tank. While you may still have some algae from time to time, too much light allows it to bloom and even take over the tank.

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Once that happens, it can be very difficult to get the problem under control. Instead of enjoying and showing off your goldfish, you'll find your time monopolized by trying to determine what kind(s) of the many types of algae have taken over the tank and what to do about it. Introducing algae-eating fish as your goldfish tank mates can help, but it's rarely a cure since they can only eat so much algae.

Watch for cloudy water

If you start noticing your tank water becoming cloudy, you may be providing too much light, either by leaving it on for too long or by having a light that's too large for your tank. Also, do not put the tank in direct sunlight. It's possible that you are overfeeding your goldfish, and the excess rotting food and feces are making the water cloudy. Try replacing about one-third of the water with fresh water every week to remove some of the excess food and waste.

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Cloudy water can become green water overnight, which indicates an algae bloom and requires a lot of time and effort to clear up, so it's best to maintain your goldfish tank well before it gets to that point.

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