Do Fish Need Light at Night?

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As an aquarium hobbyist, you may already know the importance of daylighting for your fish. Keeping a light on in your aquarium or giving your fish access to natural lighting during the day is important for their health. But should you keep a light on in your tank at nighttime as well? Here are the pros and cons.

Pros and cons of night lightning

If you are considering keeping a light on in your tank at all times, you may wonder what the risks and benefits of night lighting are for your fish.

Here are the pros and cons of leaving a light on in your tank overnight:


There is really no benefit to leaving a light on in your fish tank full-time other than being able to see your fish and enjoying the ambient lighting from the tank.

If you have live plants in your tank, leaving the light on for long periods of time can help encourage growth. But while you and the tank plants may enjoy these small benefits, they may come at a devastating price for your fish.


The risks of keeping a light on in your tank overnight far outweigh the benefits:

1. Having a light on all the time puts a lot of stress on your fish and greatly reduces their quality of life. Imagine if you could never turn the lights off and had to sleep in bright lighting. That’s how your fish feel when you never turn off their tank light.

It might be even worse for them since they’re generally used to lower lighting conditions than humans.

2. Just like humans, most fish need darkness to rest properly, while others can be more active at night and wait for darkness to feed. For these fish, not having that crucial time where they can search for food comfortably is dangerously stressful.

RELATED: Can Fish See in the Dark?

3. Depending on what type of light you are using, leaving it on 24/7 may not only provide brightness for your fish tank but also heat.

If your light is always on, it might heat the water too much for the comfort and survival of your fish. Turning the light off gives the water a chance to cool down again, regulating the temperature.

4. Too much light encourages algae growth. The faster the algae grows, the more often you have to clean the tank. Not only is this unpleasant for you but it also further stresses your fish.

How many hours can you leave your aquarium light on?

Although you shouldn’t leave your tank light on constantly, it’s perfectly fine to light your tank during the day. If you keep your fish in a room that doesn’t have a lot of natural light, using a tank light can help keep them on schedule.

It’s best for your fish if you try to mimic natural conditions by lighting the tank for 8-12 hours per day. The exact number of hours within this window will depend on what types of fish you have.

Coldwater fish need less light, closer to 8 hours per day, while tropical fish need more, closer to 12 hours. If you have both types of fish, settle for the median of 10 hours.

You should try to be as consistent as possible with your lighting by turning the light on and off at the same time each day. This helps your fish adjust to their environment and know when it’s time to sleep and eat.

Should you use automatic dimmers?

Automatic dimmers are a great way to ensure that you allow your fish a dark period for rest without having to manually flip a switch on and off every day.

Dimming also mimics natural lighting better than just turning the light on and off! Here’s a cheap one on Amazon.

NICREW Single Channel LED Light Timer Pro, LED Digital Dimmer for ClassicLED, ClassicLED Plus, SkyLED, BrightLED and Other Lights with Standard 2.5mm/2.1mm Power Connectors

If you don’t use a dimmer, you should at least invest in a light with a timer that shuts the light completely off and on. The most important thing is to make sure that your fish have some time of total darkness, just like they would in the wild.

Bottom line

No, fish don’t really need light at night. In fact, if you want to take the best care of your fish and your tank, you need to allow them a darkness period.

This allows your fish to rest, mimics their natural habitat, and prevents algae from growing too quickly in the tank.

Timers are the best way to make sure that your fish are getting the appropriate amount of light and darkness every day.

About the author

Li-ran B.

Li-ran has been taking care of fish since he was a young kid and considers himself a self-proclaimed aquatic hobbyist at heart. What started as a simple childhood curiosity quickly turned into a full-fledged passion. Currently, his new obsessions are nano aquariums and glowing fish tank decorations.