Just how important is light to your goldfish (and your tank)?

Sure, it’s nice for aesthetic reasons…

… But is it only another needless expense, or something that plays a bigger role in the health of your aquarium?

I think you’ll be surprised at the answer!

It’s time to shed some light on the subject…

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Do Goldfish Need Light, and if so What Kind?

I used to think lighting wasn’t important to my goldfish since I never kept light-demanding plants for a long time.

But this is what made me change my mind:

Yes, goldfish need light.

Goldfish have certain light requirements to stay healthy.

Specifically, they need full-spectrum light to create vitamin D in their skin.

Unless they have this, they can end up not producing enough to maintain healthy levels.

Vitamin D deficiency in fish can result in bone diseases, issues with muscle function and endocrine disruption (source).


Not only that, but their coloration can suffer.

(Goldfish pigmentation depends on adequate lighting.)

Want to pull out those deep blacks?

Strong light is essential!

If you’re still not convinced…

Get this:

Full-spectrum light actually promotes a strong, healthy immune system in your fish.

This helps them fend off sickness and disease.

Why Full-Spectrum Lighting is So Important


Standard aquarium lights don’t cut the mustard.

Only full-spectrum lighting provides the benefits of vitamin D synthesis because it emits UVB rays.

Not only are these important to your fish’s health…

… It is critical to most aquarium plants to thrive.

The problem?

Most tanks are never exposed to full-spectrum natural sunlight.

Or if they are, it is only for a short window of the day and not enough to provide lasting benefit.

Direct sunlight can also cause the aquarium temperature to spike unexpectedly and then fall, which fluctuations can cause stress to fish.

Instead, I recommend getting a good quality full-spectrum LED goldfish light for your aquarium.

Good for your fish – and good for your plants (if you decide to keep any).

Not to mention how beautiful it makes the tank look.

What is the Best Full-Spectrum Light?

For best plant growth and the most natural-looking tone, your light should have a color temperature of between 6500-8000K

I use the kind with the aluminum housing.

They don’t get very hot and they seem to be stronger than the kind with the plastic shell.

Plus, they look awesome.

Here are the sizes you can find them in, depending on the length of your tank:

The Role of Lighting in Algae Growth

Strong full-spectrum light helps encourages the growth of beneficial green algae – a great source of grazing for goldfish.

This is neat:

Did you know that it can actually help prevent some kinds of algae?

It does this indirectly by helping your aquarium plants flourish.

Having a strong network of aquarium plants helps to out-compete many strains of algae by taking away their nutrients (a concept known as competitive exclusion).

Unless your aquarium plants have lots of good quality light, they will fail to grow much and bad algae can take over.


Lighting Duration: How Much Light do Goldfish Need at a Time?

There are two ways you can approach lighting:

Number one…

12 hours a day of constant light (if you have a CO2 system and lots of plants).

OR for the planted tank with no injected CO2, Walstad recommends 5 hours on, 4 hours off, then 5 hours on again (source).

This mid-day “siesta” allows CO2 levels to rise naturally without having to add it yourself.

More CO2 = helps with less algae.

But that can be a bit of a pain to try to manage, especially if you aren’t around the aquarium all day.

I mean:

Even on and off twice a day is another chore to remember.

What if you’re ever sick or go on vacation?

For that reason I got myself a handy-dandy automatic light timer.

You won’t have to worry about turning on and off the lights manually ever again – set it and forget it!


If you don’t have plants but want a light, you may find yourself with algae issues the more light you add.  Sometimes, not always.

There are ways to deal with that too.

A magnetic algae scraper is great tool to keep the glass clean.

Or if you chronically struggle with that ugly diatom brown algae, Phosguard is something you may want to consider to get your tap water’s silicate levels down.

Oh, and don’t forget your snail cleanup crew!

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Do Goldfish Need Light at Night, or only During the Day?


It’s important that your goldfish have a day/night light cycle to mimic conditions they would have in the wild.

Leaving the light on all the time over your tank might make your plants grow like crazy…

… But your fish will suffer from insomnia!

The stress of leaving the lights on all the time can actually severely weaken the immune system of the fish.

That means they have a higher risk of getting disease.

So please never, EVER leave the lights on all night and all day for the sake of your pets.

Sleep is very important for them like it is for you.

If you’ve ever tried to go to sleep under a bright light, you know what a disturbance that is.

And not to mention, goldfish don’t have eyelids, so it’s much harder for them!

Do Goldfish Like Light for their Tanks?


When they have the right kind of light and when they have proper day and night cycles, goldfish do like light.

It allows them to see their environment and helps them develop lots of nice color.

When kept in the dark, goldfish can actually turn white as they lose pigmentation!

That said:

New goldfish are the exception.

They have been through the stress of shipping and are now in a strange place.

Having bright lights on above seems to make them more bewildered.

Some report their new stressed fish “crash around” when turning on the lights.

If that happens, you will probably want to turn them back off until they feel more settled in.

They will eventually adjust.


It’s a good idea to leave the lights off for the first day or so while your new fish acclimates to its surroundings.


Now I think you’ll agree with me when I say:

Light is an essential part in maintaining a healthy goldfish and ecosystem in your aquarium.

Plus, it also makes your tank look amazing.


Did you learn something new?

Have a burning question?

Leave your comment below!