Low pH can have adverse effects on moon jellyfish over time, especially when it drops below 7.6. This problem is common in aquariums with filtration systems that don’t allow for adequate aeration or disturbance of water.
The optimal pH for moon jellyfish is 8.0-8.2. As pH lowers below this range, the water becomes more acidic and harbors excess carbon dioxide (CO₂). If prolonged, the lower-than-optimal pH can cause pitting in the bell, eversion, and bell shrinkage in jellies. Although moon jellyfish are commonly described as being “hardy” and “tolerant” of extreme water quality levels, too extreme can and will eventually cause them damage.
A damaged jellyfish after living in <7.6 water. Photo from our Cubic Orbit 20 Aeration video.
Filters that allow for splashing and rapid movement of water through them introduces oxygen to the system, keeping the pH up by steadily off-gassing that harmful CO₂. When filters are completely submerged in water, the rate at which the water is moving through them is little to none and can negatively affect both the water quality of your aquarium and the beneficial bacteria that you’ve worked so hard to grow during cycling. If the water isn’t moving through the filters, then the filters are doing nothing to clean the water. Adequate and efficient water flow through the filters is necessary for both the water quality and beneficial bacteria to stay in tip-top shape.
Luckily, this is an easy fix!
There’s all kinds of water conditioners, additives, and buffers on the market today that are specifically made to raise pH… for normal fish tanks, however. Since jellyfish are 96% water, they are a bit more sensitive to the chemical makeup of water than normal saltwater fish. So, adding in a bunch of chemical powders and liquids, especially into a small desktop jellyfish aquarium with less than 10 gallons of volume, isn’t always the best idea and can cause more harm than good! So, don’t do it!
Instead, we recommend the following tips to help keep your pH optimal:
Adding a bubbler is an easy and worry-free fix to raise pH. Bubblers (also known as aerators) constantly introduce oxygen to the water via bubbles. Most aerators include a valve or dial to alter the rate of bubbles giving you more control, which is even better.
It’s best to place the bubbler in the filter compartment, away from the pump, and as far down to the bottom of the tank as possible. This way, the bubbles are not being sucked into the pump and have a longer path to reach the surface, releasing a bit more oxygen into the water.
Note: You do not need an air stone, if one is included. These will only create smaller, erratic bubbles that have a higher chance of getting sucked up by the pump and into the jellyfish area – which you don’t want!
Always make sure your new saltwater has a pH of 8.0-8.2. This will help raise the overall pH of your aquarium and keep it up through weekly water changes.
We experienced this problem when working with the 6 gallon Cubic Orbit 20 jellyfish aquarium, as you can see in the video below that we put together some time ago.
***At this time, we are suspending the “program” part of our Fish-less Cycling Program due to reduced staff availability. Signups will not be accepted until further notice. If you are setting up a new jellyfish aquarium, we still strongly recommend you still cycle it using the fish-less method before introducing your first jellyfish.***
Thanks for your interest in our Fish-less Cycling Program! This program was set up back in 2016 for two reasons: 1) to help new jellyfish owners have a successful start with their new aquariums, and 2) clear up misinformation floating around the internet about the cycling process and how long it takes to successfully cycle a new aquarium. Cycling a new aquarium takes time, patience, and attention to detail but it ensures your new aquarium is biologically stable and habitable for any saltwater animal; this is not jellyfish-specific issue! This blog post provides the essential information you need to know about what cycling is and how to cycle your new aquarium. At the bottom of this post (after you’ve read every bit of information and become a cycling expert, of course!), you’ll find the sign up form to participate in our Fish-less Cycling Program.
A “fish-less cycle” is the best and safest way to cycle an aquarium, as it doesn’t harm any fish or jellyfish. The goal of cycling a new tank is to establish a healthy and strong colony of beneficial bacteria in the filters to take care of waste that is created by feeding the animals (in this case, jellyfish!). The process of cycling a new aquarium is often overlooked and can create problem right from the get-go. New jellyfish owners who do not allow their tank to completely cycle before adding their first jellyfish sadly end up with unhealthy & deformed jellyfish and become confused about why they are not well. Since jellyfish are 96% water, they rely heavily on water chemistry (a.k.a. water quality) and therefore, need a biologically stable and “chemically clean” environment in order to thrive.
Cycling takes no less than 4 weeks. There is misinformation going around the Internet about how long cycling takes. Some websites claim “it only takes 10-14 days” or “two weeks.” This is wrong. The nitrogen cycle is straight forward biology and you can’t speed up biology. Even with the use of “bio-starters,” you must still cycle the aquarium and it will still take 4 weeks minimum.
Now, let’s get to what it actually means to cycle your new aquarium!
Cycling is turning a static, non-living environment (i.e. brand new tank/filters) into a biologically stable environment that’s safe for live animals.
What do we mean when we keep saying, “biologically stable environment”? Well, the filters (i.e. bioballs, rock media, etc.) of an aquarium need to have strong, healthy colonies of beneficial bacteria established within them. Beneficial bacteria = good bacteria! They take care of the waste created from daily feedings. Cycling allows these bacteria to establish themselves by multiplying and creating large colonies able to handle the waste created within your aquarium by the fish and the food being fed daily.
The Nitrogen Cycle: This is a three-step process converting ammonia (NH₃) into nitrite (NO₂) and finally into nitrate (NO₃)– all done through the bacteria. The “cycling process” is essentially the “nitrogen cycle”! All three of these compounds will be present at some point during cycling and since ammonia and nitrite are toxic to all saltwater animals (not just jellyfish), this is why cycling should be done “fish-less” and before introducing the first animals. Nitrate is a by-product of the nitrogen cycle that will always be present in your aquarium and is not toxic to moon jellyfish under 100 ppm; so, no need to worry about nitrate while cycling! It is always maintained through weekly water changes once cycling is done.
Graph estimating how the nitrogen cycle progresses over time. Taken from “The Nitrogen Cycle” by Centreville Aquarium Centre.
Fish-less cycling involves placing a nickel-sized (approx. ¾” x ¾”) piece of raw shrimp (add one nickel-sized shrimp piece for every 10g of water volume your aquarium can hold) into the filter box or compartment of your aquarium. The raw shrimp will begin to decompose and create ammonia to start the cycling process. At the same time, a starter bacteria culture is added to begin the colonization in the filters. After about two weeks, the ammonia level will rise to a peak (also known as “spiking”) and then start to decrease to zero. Once the ammonia is finished spiking, the nitrite level will begin to rise. After another two weeks, the ammonia will return to zero and the nitrite won’t be far behind. Once the ammonia and nitrite levels both return to zero, the aquarium is cycled!
Thermometer and hydrometer or refractometer – to test for temperature and salinity
Fish-less Cycling Program Guidelines – this is your weekly guide to see what the *expected* week-by-week changes in water quality (also a.k.a. the nitrogen cycle) for your tank [download the PDF below]
Screenshot taken from our EON Instructional Video Series video about cycling. Watch the video here.
Let’s start cycling!
Once your new aquarium is set up and running with new saltwater (salinity should be 1.022-1.024 Specific Gravity or 31-33ppt), add the bacteria source and two nickel-sized pieces of shrimp at the same time.
Take your baseline water quality readings – this includes temperature, salinity, pH, ammonia, and nitrite.
Test for pH, ammonia, and nitrite every week to keep track of the fluctuations in levels that indicate where you are in the cycle. Record these on the PDF guideline water quality sheet (download below).
Once both ammonia and nitrite have returned to zero after subsequent spikes, your aquarium is ready for jellyfish! (Keep the piece of shrimp in your aquarium until the jellyfish arrive. It will continue to feed the newly established beneficial bacteria until you begin a daily feeding routine with jellyfish).
DO read this entire blog post and the Fish-less Cycling ProgramGuidelines to fully understand the cycling process and how to cycle your new jellyfish aquarium
DON’T skip any part of this blog as it contains all of the essential information you need to know about cycling!
DO use new saltwater with the following baseline water quality parameters:
Temperature = 65-78°F
Salinity = 31-33 ppt or 1.023-24 SG
pH = 8.0-8.1
DON’T add any buffers, conditioners, or additives to your aquarium water before or during the cycle – these can throw off the water quality and disrupt or inhibit the cycle from starting
DO use Instant Ocean Sea Salt mix for your saltwater as it has no buffers, conditioners, or additives [Purchase from Amazon here]
DON’T use any salt mix labeled as “reef salt,” “pH balanced,” “probiotic,” or “enriched” as these tends to have extra minerals, vitamins, and higher levels of pH specific for corals, anemones, etc. in reef tanks
DO make sure your pump is plugged in, turned on, and working properly
DON’T keep your tank near windows and/or in direct sunlight to keep algal growth at a minimum
DO use freshwater labeled only as “Distilled Water”
DON’T use freshwater jugs labeled “Spring Water,” “Purified Water,” or anything else to mix your saltwater or for topping off
DO add distilled/RO water to compensate for evaporation (evaporation causes salinity to rise; adding freshwater helps to bring it back down)
Evaporation is noticeable when the water level is lower than where it started
DON’T add distilled/RO water near the filters – this can completely wipe out your growing bacteria colonies
Only add freshwater to the main viewing area
DO record your weekly test vial readings via pictures with the color chart
DON’T use test strips as they often give unreliable readings
DO start the cycling process with a newly setup aquarium.
If your aquarium has been running with saltwater & the bio starter bacteria for longer than a week, you will need to dump the water and start over with all new saltwater & new bacteria.
DON’T perform any water or filter changes during cycling – this can disturb the growing bacteria and disrupt the cycle
DO keep an eye on the piece of shrimp in your tank – sometimes it can completely disintegrate before the cycle is over and will need to be replaced to keep the ammonia production up
DON’T freak out if your cycle isn’t exactly on track – every cycle is different and sometimes an aquarium needs an extra week to catch up
DON’T add a bubbler if you own a Cubic Orbit 20 jellyfish aquarium before or during the cycle – aeration can inhibit the cycle from starting
Things that can delay or disrupt the cycling process
Starting with a pH higher than 8.2 can inhibit the cycling process from starting by disturbing the bacteria. The pH of an aquarium will naturally drop during the cycle – which is normal! – and needs to be left alone to do its thing until the cycle is done.
Starting with salinity too high or too low can also inhibit the cycling process from starting by disturbing the bacteria. The optimal salinity range for moon jellyfish is 31-33 ppt or 1.023-24 SG, which is perfect for cycling.
We’ve put this 3-part video series together to help you set up and keep your jellyfish in the Cubic Orbit 20! It’s a great little tank and if you follow a few of our tips, you’ll be super successful!
There have been situations where folks started cycling their tanks and then the cycling process was interrupted for some reason. Perhaps you interrupted the cycle due to premature cleaning of the tank and/or changing of some filters or water? Or, you went out of town for a few days and the tank wasn’t receiving any food and therefore the beneficial bacteria starved and left you with a zero population? Whatever the reason, you now got back on track and finished cycling the tank. Yay! Now you finally have a zero reading for ammonia and nitrite! Great! So, you order some new jellyfish and they go bad after a few days? What is going on? You did what you were supposed to and cycled your tank. Why are your new jellyfish so sad? Read on….
If you have already interrupted the cycling process, then you need to do a few more steps before your system is safe for jellyfish. Your nitrate & phosphate levels have skyrocketed because you have prolonged the normal 4-6 week cycling process & no substantial water changes have taken place. (Remember, after your system cycles, you are supposed to do a 20% water change and then get on a weekly maintenance schedule where at least 10% of the water is being exchanged every 7 days) But, because your system didn’t cycle in a timely fashion, your nitrates and phosphates are very high–toxic. Again, although it is great that you no longer have any ammonia or nitrite in your system, your nitrates and phosphates are through the roof because you haven’t changed out any water! You may be experiencing cloudy water because of these high levels (cloudy water can also be caused by a bacterial bloom).
Cloudy water due to high nitrates & phosphates from a prolonged cycle.
These high levels will cause your new jellyfish to shrink and/or fall apart. Nitrates can be removed by exchanging the old water out with new saltwater. There are some liquid drops available on the market now that will remove the phosphates, Ultralife and Phosphate Rx, but you still need to attend to those high nitrates. Best thing to do is to conduct a 20% water change every other day until your nitrates drop from 80+ppm to under 40ppm but only if your system is already fully cycled and your nitrates are over 80ppm. I know this seems extreme, but once it’s done, you’re good! Water chemistry is an art, but if you have a system that has a fully functional mechanical, chemical and biological filter in place, it will do the job for you over time once you get it balanced and eliminate those nitrate and phosphate levels that have built up over an extended period of time (over 8 weeks) while you were waiting for your system to biologically cycle.
Moon Jellyfish repairing himself after a toxic round of high nitrates and phosphates. Holes are repaired in the bell and he’s become whole again.
So, to recap, if you had an extremely long period of cycling (over 8 weeks), then you need to test your nitrate and phosphate levels. If you are getting readings of 80+ppm for nitrate and/or 2.0+ppm for phosphate, you need to conduct several water changes over a week to bring them into range. You want to achieve levels of under 40ppm for nitrate and under 0.5ppm for phosphate.
If you need some assistance with this process, please email us @ moonjellyfish.com@gmail.com and we’ll help you through it. It’s just some water changes…no big deal, really. Hang in there…you’re almost home free! Once you correct the water chemistry, your jellies will instantly start repairing themselves and get back to a healthy state.
If they do, I’m sorry to hear that, but don’t despair just yet. Once you determine the problem & fix it, the jellies can bounce back and repair themselves in no time! Here are the top 5 reasons jellyfish will start to fall apart…
1. Improper filtration and/or incomplete cycling of your filters.
2. Ammonia spike.
3. Not Acclimating your Jellyfish Properly
4. Improperly making up your saltwater
5. Heavy metal contamination.
1. Improper filtration and/or incomplete cycling of your filters.
If you haven’t properly cycled your tank, then you most likely have toxic levels of ammonia and/or nitrite in your water. This can happen when you initially set up an aquarium and add jellyfish (or any life forms, for that matter…this is not a jellyfish specific issue, but a standard fish or coral tank issue. You must take the time to properly cycle your aquarium no matter what animals you choose to keep in it). Once jellyfish are added to the tank, they begin to produce ammonia. Once ammonia starts to build up, you need to have a way to eliminate it. This is why proper filtration is important. A properly filtered aquarium will have a biological filter in place, which will remove the toxic ammonia and nitrite by way of the beneficial bacteria that populate the filter media (i.e. bio balls). If you do not have beneficial bacteria actively removing the ammonia and nitrite, then the water becomes toxic and the jellyfish will soon begin (within 2 days) to disintegrate like the pictures demonstrate.
Ammonia & Nitrite levels demonstrating the middle of a nitrification cycle. This is a very toxic situation. Jellyfish will fall apart if subjected to these levels of toxicity.
2. Ammonia spike.
Why are you having an ammonia spike even after you’ve already cycled your tank? An ammonia spike can occur if you stopped feeding your tank for any reason. Sometimes folks let the aquarium go down, or let it run without any animals in it for awhile like if they go on vacation or take some time away from keeping jellyfish, or they don’t have jellies in it for several days for whatever reason. This leads to an ammonia spike because your beneficial bacteria in you filter box didn’t receive any ammonia to eat—your system wasn’t creating any ammonia because you had no jellyfish in it & subsequently weren’t feeding any jellyfish. This means the beneficial bacteria went with out food (ammonia) and starved to death. So, if you then add jellyfish to the tank when you get back from vacation (or whatever), there is no beneficial bacteria available in the filter box to eliminate the toxic ammonia & you experience an ammonia spike and shredded jellyfish as the pictures show.
If you do go on vacation, or take more than 3 days away from having jellyfish in your tank, you can alway place a small, 1/4″ piece of raw fish or shrimp in the filter box to continue to decompose and create ammonia for the beneficial bacteria to feed on while you’re away. When you return, always take an ammonia reading and remove the piece of raw fish or shrimp before adding new jellyfish to the tank. Make sure your ammonia and nitrite levels are at zero before acclimating any new jellyfish into your tank.
An ammonia spike can also happen if you interrupted the cycling process by cleaning the tank, changing any mechanical or chemical filters, or conducted any water changes prior to the tank completely finishing its cycling process. Do not interrupt the cycling process. I know it’s tempting to want to get the sides & bottom of the tank clean. The algae growth can be unsightly, but remember, you are creating a living environment from a static one. Life can be messy! Let nature take it’s course and be patient– I know it’s hard, but it is necessary. You can clean the tank all you want after the cycling process is over! If you interrupt the cycle, it can take almost 3 times as long to get it back on track an in a non-toxic state. Be patient. It’s worth the wait!
3. Not Acclimating your Jellyfish Properly
You are receiving jellyfish that are coming from a pristine environment. When you receive a shipment of jellyfish, the water quality parameters are most likely different from yours. You must take the time to acclimate the jellyfish in the shipping bag to the temperature of your system. After 10-15 minutes of floating the bag so the temperatures equalize between the bag and your tank water, acclimate them to your water quality (pH, salinity), by conducting small water changes in the bag over 45 minutes to 1 hour. Don’t take all night doing this step. The jellies need to get out of the bag and into a moving environment. Acclimation shouldn’t take more than 1.5 hours from start to finish. If it is taking longer than that, then there is another problem at hand that needs to be addressed.
4. Improperly making up your saltwater
If you are making up your saltwater with tap water, your jellyfish will fall apart. Tap water has heavy metals in it that the jellyfish cannot tolerate. You must make up your saltwater with RO, RO/DI, or distilled water for it to be safe for jellyfish, much like a reef tank.
If you are not aerating your saltwater for at least 24 hours in a bucket with a small submersible pump, then you most likely are adding undissolved salts to your tank. The jellies don’t do well with undissolved salts. Please read our blog post that covers this topic in depth: “Problem with Your Jellyfish? Undissolved Salts Could be the Culprit”
5. Heavy metal contamination.
Do not use metal utensils or tools with your saltwater jellyfish aquarium. Only use plastic tools. Always wash your hands before dealing with your jellyfish or handling the jellyfish food. Zinc, brass, lead & petroleum products (sometimes found in soaps and lotions) will add heavy metals to your system. The jellyfish will fall apart if you introduce them into the water. Also, I should mention that aquarium heaters can get old– moreover, their seals can get old and crack. This can allow water to leak into them where the metal heating coil is located and other metal parts. If you have an old heater, check it for any visual signs of rust on the heating coil. If you see rust, throw it away and purchase a new one.
Send us your problem jellyfish pictures and we’ll diagnose the problem and tell you how to fix it. We’ll also write a new blog post about it so we can inform and help others that may be experiencing the same problem!
Send your pics to moonjellyfish.com@gmail.com
•••
Have you had an unusually long cycling process? Are your new jellyfish shrinking fast even after the tank finally cycled?? Please read our blog post next week for answers.
Large 10″ diameter Moon Jellyfish– This jellyfish has been raised in one of our customers tanks from 3″ diameter to 10″ diameter solely on our Frozen Jellyfish Food (feeding once a day).
Are your jellyfish shrinking, getting thin and flattening out???
Here are 5 reasons why that might be…..
1. Feeding Non-nutritious food
One of the most common problems when keeping jellyfish is keeping them properly fed. Without a consistent supply of nutritious food, they will become weak and thin. Malnutrition causes listlessness and infrequent belling or pulsing, leaving you with inactive jellyfish that just float around the tank like pieces of tissue paper. Not pretty. Not elegant. Not fun! Your solution is to feed them jellyfish food that is nutritious & to feed them the proper amount. There are a lot of feeds on the market for fish and corals and you may think that they will work for jellyfish. Not the case. Reef Nutrition has some amazing feeds for filter feeders and some of what they have to offer are good supplements for jellyfish, but not strictly meant for a main food source.
Jellyfish are not goldfish & you cannot simply sprinkle some food in every other day or so. They need to eat each day and they need to get a good amount into their systems with each feeding. See our blog post Knowing How Much to Feed Your Jellyfish for guidelines & pictures of what a well fed jellyfish looks like. Without enough good food to eat each day, they will become thin and lazy.
3. Your Flow is too High—or Too Low.
If your jellyfish aquarium has adjustable flow, you may need to fine tune it. If the flow is too high, the jellyfish may not be able to keep the food on their tentacles as they whiz around the tank and this means they are not ingesting the food. This leads to underfed jellyfish, which leads to lazy and shrinking jellyfish. The same goes for low flow. If the flow in your tank is so low that the jellyfish cannot properly bell and keep themselves suspended, then they will not feed properly. Again, this leads to malnutrition and shrinking jellyfish. Jellyfish need to bell efficiently in order to move fluids and food into and throughout their system.
4. Your Jellyfish Aquarium is Not Cycled
If your aquarium is not biologically cycled then your water quality is toxic (you have ammonia and/or nitrite levels above zero) and the jellies will be stressed because of it. Jellyfish are 96% water, so if your water quality is suffering, so are your jellyfish. They will not eat much, if at all, and this leads to shrinking jellyfish.
5. Your Salinity is Too High
When your salinity is too high, the jellyfish will cease to eat. Keep your salinity in check–everyday if necessary–so your jellyfish can feed properly without the stress of spiking salinity levels. If you haven’t yet read our blog post about hydrometers and the inaccurate readings they can give….read it now. The plastic hydrometers on the market tend to have variable readings. Have your hydrometer tested at your local fish store to be certain that yours is giving you accurate readings. Again, if your jellyfish are not getting enough food each day, they will shrink.
And a word about vacations, weekends & days off from feeding….
If your jellyfish are healthy and being fed normally and on a regular basis with nutritional jellyfish food, then you can safely get out of town for the weekend. They will be fine given they have full stomachs 5 days out of 7.
Another common problem concerning salt levels in your jellyfish aquarium, besides inaccurate hydrometers giving a false reading, is how the saltwater is made. Undissolved salts can also give you an inaccurate reading which is a problem since jellies are very sensitive to salinity changes & high salinity levels can also impede their movement, eating and overall cellular activity. It is important to know what your salinity is and how it changes over time.
The point I need to make here is about how you make up your saltwater with distilled or RO water.
Always prepare the saltwater at least 24 hours ahead of time. Adding undissolved salts to your jellyfish aquarium will damage the jellies tissue and can cause them to be very still and not bell or pulse much…their bell can curl under and they will fully retract their tentacles and not eat because of the tentacle retraction. They will look and be sad….sad jellies. Also a dusty film of white on the interior of your tank will form, which can make the tank look cloudy.
Properly aerating saltwater involves a small submersible pump called a powerhead, and a bucket. A simple “bubble wand” or “bubbler” will not degauss and dissolve the salts completely. I know the words “aeration” and “bubbler” tend to go hand in hand, but in this case it’s just not the right tool for the job. You need more mixing power in the water which a powerhead can give you. Once you add the desired amount of salt, vigorously mix for a minute or two with your hand or 2 foot length of PVC pipe as a stir stick. After that, you can let the powerhead pump ( in this scenario a Lifegard 800 is perfect!) do the rest. See diagram above to see how to set this up in a 5 gallon bucket. It could be any size bucket as long as you position the powerhead pump at the water level allowing it to pull in air as it mixes. You want the water and air to be churning vigorously.
If you have some residual stuff still swirling around the bottom of the bucket after 24 hours don’t worry about it. Just leave it there and don’t try and mix it into the water you will be using for a water change. You can rinse that out and get rid of it before making another batch of saltwater. It’s just undissolved minerals and is totally normal.
Important Side Note!!
Never use tap water to make up your saltwater–not even if you use some sort of water conditioner that removes chlorine. There are heavy metals, pesticides and ever more increasing levels of pharmaceuticals in city tap water supplies. No sort of chemical conditioner will eliminate these things from the water. You must use distilled or RO (reverse osmosis) water. Do not use “spring water” or “mineral water” or “drinking water” — it must say “Distilled” or if you are purchasing from a water store, it must be RO or RO/DI.
As you populate your eon jellyfish tank with jellies, you may sometimes notice a jelly acting differently; belling oddly or sometimes infrequently. Is that jelly sick? Should you take some action to make it better? Not necessarily. First of all, jellies don’t get sick, per say; however, they can plateau in their development.
Take a look at your other jellies. Are they behaving in the same fashion as the jelly in question? Take some water quality readings and see if they are in range or not. Correct any levels that are off and wait a day or two. The jellies are 96% water. So, if your water quality checks out A-OK, then your jelly in question could be taking a personal day—having personal issues. This does not mean you need to take action on your whole system. If your water parameters are in range, be patient and keeping observing.
We have noticed over the years that sometimes a jelly will sort of plateau and change behaviors for up to two weeks and then get back to normal. Some jellies grow quick and fast and are always in action, but then their growth rate slows down and they can plateau. Some don’t grow at first and then take off later in life. Be patient with your jellies as they settle into your system and with your maintenance practices. It’s good to be on the ball observing their health and wellbeing; however, think about your tank as a system–an aquatic system. Don’t be quick to judge one or two “off” days with a jelly here or there. And do not go the route of forcing more food into the equation thinking that is the answer. Let nature do its thing and just maintain good water quality and maintenance practices. These guys are resilient and given the chance, they can rebound nicely in a well-kept environment.
Another thing to consider is that you are observing animals in a closed system and natural selection is taking place in front of your eyes! The stronger jellyfish will bell more, eat more food and grow faster and bigger. While, at the same time, the weaker jellies will grow more slowly and the very weak jellies will stay the same size as when you first introduced them, or will shrink. This is completely normal. We liken it to the “varsity”, “junior varsity”, and “bench warmers” of the jellyfish world. It is to be expected. In very rare cases will all the jellyfish remain the same size in a closed system.
P.s.
…in some cases they take a personal day for the rest of their lives and there isn’t anything to be done. They can still eat and live and be just fine. Embrace the existentialists!!!
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