How Long Should I Leave the Lights On in My Jellyfish Tank?

Eon on a table

If you’ve got one of our beloved EON jellyfish tanks, then you’re probably familiar with the color-changing LED lights we outfitted for you. They help make your little jelly friends easier to see when they don’t have food in their stomachs, and they give you the opportunity to throw yourself a jellyfish disco party. However, like everything else, they can also cause problems when you use them too much.

Problem 1- Algae

If your tank has been set up for more than a week or two, you’ve probably noticed some green or brown algae starting to appear on the walls or floor of your tank. That’s perfectly normal—actually impossible to avoid—but it does need to be scrubbed off before it builds up too much. What’s the point of having pet jellyfish if you can’t even see them through all the algae, right? It can also have harmful effects on the water quality when it gets too thick.


Algae is photosynthetic, like plants, so it needs light to grow and the more light you give it, the more it will grow. You’ll probably notice one of the first places it starts to really build up is just over the light strips on the floor of your tank. So while you can’t stop it from showing up and growing, controlling the amount of time you keep your lights on will keep algae growth somewhat in check.

Problem 2- Your Jellies Themselves!

While jellyfish don’t have brains or eyes, they can perceive the difference between light and dark using small light-sensing organs called rhopalia, which are located around the perimeter of their bells.



As such, like many animals, some of their internal functions are based around daily light cycles. It is important to your jellies’ health that you replicate these light-dark cycles with your tank’s LEDs.

The Solution- A Simple Timer!

screen shot 2019-01-28 at 1.38.05 pm

Rather than trying to force yourself to remember turn the lights off in your tank every night, you can just buy a timer and set it so your light will go on and off automatically. They’re cheap (many effective models are less than $10) and available online or at pretty much any hardware store. Just plug the timer into your electrical outlet, then plug the lights into your timer, and set it for your desired time.

We recommend 12 hours light, 12 hours dark, but it’s up to you which specific times of day you choose.

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