5 Things that can cause your Jellyfish to Shrink

Large Moon Jellyfish
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.

2. You Are Not feeding Enough Food (of the nutritious kind)

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.

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