What is This Baby Jellyfish in my Reef Tank and Where did it Come From?

It happens more than you would think. You’re gazing into your saltwater aquarium and all of a sudden you observe something darting around- it looks like a jellyfish. But what is it really and how did it get here?

As jellyfish experts, we hear this question a lot. We’ve compiled a guide to all of the different jellyfish hitchhikers found in marine aquariums!

Clinging Hydromedusa (Cladonema Sp.)

This species is a very common hitchhiker. I frequently see them pop up in new aquariums, especially ones with lower flow. Their hydroid stage can hitchhike in on live rock, frags etc. What you most typically see is the Medusa, or the jellyfish stage. They start as tiny rocket ship shaped Jellies and eventually attach themselves to the glass or rocks. They’re typically considered harmless in a reef tank setting, and will likely disappear on their own. The only time they pose a threat is when they take residence in larval fish operations or seahorse tanks. Cladonema hydroid jellyfish saltwater aquarium

Upside Down Jellyfish (Cassiopeia sp.)

This species is a little less common than the species above. Upside Down Jellyfish are a true species of jellyfish, and actually grow up into fascinating and neat creatures. They can be a bit of a pest when they hitchhike into your aquarium, but they’re essentially free jellyfish!

The first think you typically see are tiny 1/4″ sized brown jellyfish flapping around your tank. Like the jellies above, Upside Downs typically stow away in their polyp stage. They are small and anemone like, almost resembling an Aiptasia. This polyp stage can be irritating to corals or fish if they get out of hand. Baby Upside Down Jellyfish in my Reef tank

Day old baby Upside Down Jellyfish
Upside Down Jellyfish polyp hydroid reef tank
The polyp stage of Upside Down Jellyfish

Honorable Mention: Benthic Comb Jellies

Comb jellyfish aren’t true jellyfish, but Ctenophores. They’re known for the iridescent rainbow colors they produce. So it comes as a bit of a surprise to learn that some of these ctenophores live attached to other organisms. They very closely resemble flat worms, and most aquarium keepers would assume that’s what they are. In actuality, they’re totally harmless and incredibly fascinating.

These enigmatic creatures are often found living on leather corals or starfish. The next time you buy a wild collected leather coral, check to see if there are benthic ctenophores living on it. A tell tale sign are the spider web like tentacles they release out into the water. These webs don’t sting, but actually use sticky fibers to collect plankton floating by.

What do Healthy Jellyfish Look Like?

Jellyfish are strange and very foreign creatures. They’re often compared to alien spacecraft, and deservingly so. Unfortunately, these enigmatic creatures don’t have brains or mouths to tell us when they’re upset. As jellyfish guardians, we have to be able to tell the difference between a healthy jellyfish and a sick one.

For this post, we’re going to be using the Moon Jellyfish for all of our examples. Other species may vary slightly, but should be very similar.

What does a healthy jellyfish look like?

A healthy jellyfish should have an even, round bell. Their bodies should be fairly thick, and smooth. A happy moon Jellyfish will have hundreds of tiny fringe tentacles at the edge of the bell, and four mouth arms in the center. It should pulse once every few seconds.


In the above photo, notice how there are tons of long, hair like tentacles at the edge of the bell. These “fringe tentacles” are a good indicator of health. They should be long, relaxed and flow smoothly as the jellyfish pulses. They do tend to retract these while eating, so don’t be alarmed if they temporarily disappear!

Also notice the width of the bell. This is exactly how wide a healthy Moon Jelly should be. Thinner ones are less nourished, and may not be getting enough nutrition. IMG_1013.jpg

Note that the bells are round and very smooth. The jellies maintain a sort of half circle form. They aren’t thin like plates, but also aren’t balled up into a sphere. Both extremes are bad signs.

We hope this post can be used as a reference guide for your own jellies at home. Stay tuned, as our next post will be on common jellyfish ills and ails.

At the Jellyfish warehouse, we put the highest level of effort and research to create happy and healthy jellyfish for the home aquarium. You can purchase your own here: Jellyfish Warehouse

My Jellyfish Has Holes in it: How to Fix

Jellyfish are 95-97% water. Naturally, they are quite delicate. If they are not treated well or handled properly, they can develop rips or holes in their bells. Lets explore the most common reasons for holes, and how to fix them.

Shipping damages: This is one of the more common ways you may experience jellyfish with holes. Shipping can sometimes be stressful on jellyfish. Improper packing of jellyfish can make this worse. Your jellyfish should arrive bagged with no air or bubbles in the bags. The reason for this is that the air will break up into bubbles and get trapped in the jellyfishes’ bell. The bubbles will force their way out, creating holes. If your jellyfish arrive with holes in them, contact the company you purchased them from, and let them know what happened. At the Jellyfish Warehouse, we pack our jellies very carefully, and professionally. All of our jellies are packed with no air, and any small bubbles are removed.

How to fix: Holes caused from shipping should heal rapidly. The cause of the holes has been taken out of the equation, so the jellies should be able to heal in their new home. Feed them every day, or even twice a day to encourage repair. Jellyfish fuse holes closed with surrounding tissue, so don’t be surprised if your jelly looks a little smaller once its healed. Feeding them often will help them grow back to normal size.

Sharp or rough objects in the tank: Jellyfish have very delicate skin, and don’t tolerate sharp or rough objects in their home. This is why most jellyfish tanks are completely empty. It is highly unrecommended to add decorations or rocks direct

An Atlantic Sea Nettle with a large hole caused by bacteria.

ly in your jellyfish tank.

How to Fix: Remove the culprit item from the tank. The jellyfish should heal quickly after this. Follow similar instructions as above, feeding often.

Dirty tanks/ bacterial infections: Jellyfish like a clean home (don’t we all!). Left over food can sit and rot at the bottom of their tank, leading to build ups of bacteria and other nasty microbes. We recommend you wipe down the inside of your jellyfish tank weekly, and remove any uneaten food. Keep a good schedule of 25-50% water changes once every two weeks.

How to Fix: Do a good cleaning of the jellyfish tank. Wipe down all inside surfaces and remove and debris or detritus. Perform a 50% water change. Then let the jellyfish heal. Feed well, but be sure to remove uneaten food.

Jellyfish have amazing abilities of regeneration and healing. Small holes can often close up in 24-48 hours. These holes do not usually leave scars or signs of injury. Once your jellyfish is healed, it should look like nothing ever happened! Happy jellyfish keeping!

You can purchase your own jellyfish and jellyfish aquarium at The Jellyfish Warehouse


How to Lower Nitrates in a Jellyfish Aquarium

Nitrates are likely the most disliked molecule in the aquarium world. They’re a result of food and waste in your aquarium. But unlike ammonia and nitrites, nitrates won’t go away on their own. We’ll explore the reasons why nitrates are undesirable and some easy ways to get rid of them! 

What are Nitrates and Why are They bad?
Nitrates are the by product of jellyfish waste (jelly poop!) and uneaten food being broken down. Jellyfish will release highly toxic ammonia, which is quickly broken down into nitrites and eventually nitrates by friendly bacteria in your aquarium. But under normal circumstances, these friendly bacteria can’t break down nitrates. More on that below.

These nitrates will build up over time, which can eventually impact your jellyfish. In low levels, nitrates won’t bother your jellies. But as those nitrates creep up, it will begin to impact your jellies. Based on your nitrate readings, these are the results you can expect:

0-10 ppm nitrates: Happy jellies! 

10-20 ppm nitrates: Happy jellies but slower growth. 

30-40 ppm nitrates: Significantly stunted growth, jellies may stop growing all together. 

50+ ppm nitrates: Past this point, your jellies may actually start shrinking in size. 

How do I Measure Nitrates? 

Nitrates can be quickly measured with a nitrate test kit. We highly recommend the Nitrate test kits by RedSea. These kits are renowned for their accuracy and reliability. We highly recommend stealing clear of test strips or other all in one type tests, as these tend to be unreliable and inaccurate. 
When jellyfish are exposed to high levels of nitrates (40ppm+) for extended periods of time, it can shorten their lifespan. So it’s best to keep those levels low! If you have high nitrates, it’s nothing to panic about! Let’s look at some ways to lower nitrates and keep them low.

  1. Water Changes: This is the oldest method in the book, and the most reliable. Nothing beats a reliable and consistent water change schedule! You should try to change around 20% of the water in your jellyfish tank every 1-2 weeks. A regular water change schedule should keep your nitrates very low on its own. If your nitrates are already high, you can do larger water changes to cut them down. We recommend doing 50% water changes every 2 days until your nitrates are in a good range. Larger water changes could be too stressful to your jellies so stick to 50% every two days.
  2. Add some Matrix media by Seachem: Matrix is a highly porous filter media produced by the company Seachem. It has an incredible amount of surface area, which allows all those friendly bacteria to colonize. The center of Matrix is dense, meaning it can house bacteria that don’t like oxygen (anaerobic bacteria). These new bacteria can effectively reduce nitrates. Packets of Matrix fit perfectly in the outer compartment of your Orbit tank!
  3. Lower your feeding: We all love to feed our jellies and see them grow. But sometimes we feed them too much. If you’re feeding JellyFuel, your jellies only need a few pellets of food each. 
  4. Remove uneaten food: Food that isn’t consumed just turns into nitrates, without being useful to your jellyfish. Try using a feeding pipette to blow extra food around. The jellies may continue to eat. Any more food that settles to the bottom can be removed. 
  5. Don’t add unnecessary bacterial supplements: some companies will try to get you to add bacteria-in-a-bottle type products on a regular basis. These can do more harm than good, however. Bacteria need food to survive. So only so many bacteria can live in your tank, before they start to starve. Continuously adding bacteria means many of them will die, and just end up producing more nitrates. It’s a good idea to add some beneficial bacteria when you start your tank. But once they’ve seeded your tank, there’s usually no need to add more. 

Conclusion: Nitrates aren’t all that bad, but it’s good practice to keep them lower than 20 ppm. Doing so will ensure your jellies are healthy, growing and love long lives. Water changes are the easiest and most effective for removing nitrates. Feeding sparingly goes a long way! 

You can get your own jellyfish and jellyfish aquarium at the Jellyfish Warehouse. We’re always happy to answer any questions you have. Feel free to email us at any time: Email us!

Blue Blubber Jellyfish for Sale?

Over the years the Jellyfish Warehouse has sold Blubber Jellyfish (Catostylus mosaicus). They are without a doubt one of the most iconic jellyfish around. With vibrant and varied colors of blue, white, burgundy and black, how could they not stand out? These incredibly active jellies quickly express how they earned their name. Like blobs of blubber, they quickly steam their way around the aquarium, often running into things. They win the hearts of any and all observers. Despite this, they have a dirty secret.

Blue Blubber Jelly
Blubber Jellies don’t do well in captivity. We have spent countless hours researching and testing ways to try and keep these jellies happy. Our efforts came to no avail. These mesmerizing creatures simply weren’t doing well. Let’s look at some possible reasons they don’t make good jellies to keep. After that, well take a look at some jellies that are proven to thrive in captivity.

  1. These jellies need a ton of space. Blubber Jellies love to race around their tank. Unlike other jellyfish, they prefer open and wide tanks. They should be kept in large tanks, where there is less of a chance they will bump into something.
  2. They consume a ridiculous amount of food. Jellies this active need lots of food to fuel their speedy behavior. Blubber Jellies have really small mouths, and need to be fed live baby brine shrimp and rotifers. They have to be fed several times a day, so they are constantly full of food.
  3. All of them are wild collected. Blubber Jellies don’t breed well in captivity, even under public aquarium care. Because of this, all of the specimens found for sale are collected from the wild. They have a hard time adapting to life in captivity.

Blubber Jellyfish are beautiful and stunning creatures, but they don’t belong in home aquariums. For this reason, the Jellyfish Warehouse has stopped selling Blubber Jellyfish. We offer a wide variety of captive reared jellyfish that do phenomenally well in captivity. Consider some of these instead of Blubber Jellyfish.

Lagoon Jellyfish: The closest in shape and appearance to Blubber Jellies. Lagoon jellies are easy to keep and fun to watch.

Fried Egg Jellyfish: These exotic jellyfish are surprisingly easy to keep and never short of interesting. They’re very ornate and colorful.

Flame and Ice Jellyfish: These two species are closely related and come in orange and white colors, respectively. They’re a hardy species that bounce back quickly.

These jellyfish can be purchased on our website The Jellyfish Warehouse

Do Immortal Jellyfish Really Live Forever?

At the Jellyfish Warehouse, we get a lot of questions about the Immortal Jellyfish, Turritopsis nutricula. We’ve also had the chance to keep these lovely creatures twice. So do these odd jellyfish live up to their name or are they a just a sting?


Turritopsis dohrnii on the left, and Turritopsis nutricula on the right.

The Immortal Jellyfish is a group of jellyfish, with two species being of interest. Turritopsis nutricula, and Turritopsis dohrnii. The first species there is native to the Atlantic Ocean, whereas the latter is found in Japan. These jellies have earned their immortal title through their odd and fascinating life cycle. As a human, you probably started as a baby, and then progressed into a child, a teen and finally an adult. What if you could transform right back into an infant? Turritopsis can do just that! They curl up into a ball and transform back into their larval polyp stage. From there, they can stay as polyps or transform back into jellyfish.

This diagram shows the process of Turritopsis reverting back to the polyp stage.

So does this mean they are truly immortal? Well, scientists are not entirely sure how long these jellies can do this. So far, it seems like the answer is: indefinitely. These jellies can still die, however. If they are one-hit KO’ed, they will simply perish. The key is if they have been injured, but are able to escape. That injury is typically what initiates the process of reversing.


As scientists continue to study these enigmatic jellies, we
will begin to understand just how long they can live, and whether or not they can truly stop the clock.


You can buy your own pet jellyfish and jellyfish aquarium at our online store: Jellyfish Warehouse


Photo credits:







How to Care For Comb Jellyfish

Comb Jellies are a fascinating and captivating sea creature. Their beautiful light-show of colors draws the attention of crowds . These odd jellies appear to almost be living spaceships, with colors pulsing up and down their bodies. What are these beautiful weird things and how do we care for them?

Comb Jellies are Not True Jellyfish

Comb jellyfish
The Comb rows are visible here, with blues and greens shining.

We often refer to these guys as “jellies” and not jellyfish because they are not actually true jellyfish. They are actually considered Ctenophores (ten-oh-fours), which is a group of stingless marine creatures. That’s right, they have no ability to sting whatsoever. Unlike Moon Jellyfish, which have very little sting, Comb Jellies substitute sting with sticky tentacles. Think about those sticky hands you would buy in a quarter machine as a kid. Comb Jellies also lack that characteristic pulsing motion that jellyfish have. Instead, Comb Jellies use eight rows of combs, or rows, to bat their way through the water. These combs beat back and forth quickly, and allows the jelly to hover, and have a full 360 degrees of motion.


Their Beautiful Rainbow Color Isn’t bioluminescence

comb jelly 3
A Comb Jelly under a white LED flashlight, with a black background. 


Comb jellies are famous for the stunning rainbow effect they display. Contrary to popular belief, this is not bioluminescence. The jellies are actually breaking up and refracting light, just like a prism would. This is important because they will not display this affect in the dark! To get the greatest refraction effect follow these guidelines:


  • Use a bright white light. White light is a combination of all the light colors. This will allow the jellies to create a true rainbow of colors.
  • Use a close source point. LEDs are a great example of this. You want a lot of light coming from a small source.
  • Add a dark background. This will really help the colors pop, and help you see the jellyfish better.


How to Care For Comb Jellies

The first thing to note here is that we sell Mnemiopsis Leidyi. This is one of the most common and definitely the hardiest species of Comb Jellies available. They are found in many places around the world, including the Atlantic. We collect and find these Comb Jellies in all seasons. They are incredibly versatile, and can exist in waters ranging from 55-78°F, and salinities of 1.020-1.026. With years of research, we have found the most optimal conditions to keep your comb jelly healthy and living the longest.

  • Keep your jellies in stable aquariums with no ammonia. Many jellies are tolerant of ammonia, but Comb Jellies cannot stand it. Only add Combs to tanks that are well cycled. Additionally, pH swings can be very damaging to Combs. Monitor the pH often.
  • Keep them cold. When kept at a temperature of 60-65°F your Comb Jellies will have much slower metabolisms, and their life span will be extended significantly. Additionally, the cold water will limit harmful bacterial growth.
  • Feed them a varied diet occasionally. It’s best to feed your Combs freshly hatched baby brine shrimp on a daily basis. Switch it up every now and then with frozen rotifers and live copepods. They will appreciate the snack!

Literature used to suggest Mnemiopsis Comb Jellies would only live two months. Using the three methods above, we have managed to keep our Comb jellies for well over a year in captivity.

Care Requirements Summed Up

Temperature: 55-78°F, Optimally 60°F

Salinity: 1.020-1.026

Ammonia: 0 ppm

Best Jellyfish Tanks: Orbit 20, Pulse 80, these jellies stay around 2″ long, Orbit & Pulse have ports for a mini chiller. Set flow to very low.

Diet: Will need live baby brine shrimp as main staple. Frozen/ live rotifers and live copepods are good options as well.


Other Species of Comb Jellies

Lastly, there are a few other species of Comb Jellies. They may have special requirements, or are difficult to get ahold of.

Sea Gooseberries: These Comb jellies are a small, round creature, with two long net-like tentacles. They are straightforward and easy to care for, but require a chiller, as they are a coldwater only species.

Beroe Comb Jellies: These are very bizarre jellies, and seem to poses a mouth. This “mouth” allows them to swallow other Comb Jellies (like mnemiopsis) whole. Their diet actually consists only of other Comb Jellies, making them very difficult to feed. They are also extremely delicate and only the most expert jellyfish aquarists should attempt these.

You can buy your own pet Comb Jellyfish and jellyfish aquarium at our online store: Jellyfish Warehouse