Problem with Your Jellyfish? First Order of Business… Salinity!

I recently had the opportunity to meet and speak at length with some new local customers who came in to learn how to keep jellyfish as pets.  Payam, Lauren and their little dog Ted came down to the lab to see just what is involved with keeping jellyfish and maintaining a jellyfish aquarium.  It was super to spend time with them and show them the ropes!  It was then that I realized that most of the questions they had are the same questions a lot of folks send my way via email. So, I will start to shoot quick blog posts every week that cover these questions– most of which are not jellyfish specific questions, but standard aquatics questions that can be answered fairly easily and quickly.  And, I will certainly get to the more specific jellyfish inquiries which will help you, as a jellyfish owner, begin to recognize and identify certain issues that can arise while caring for these beautiful animals and how to correct the problem right away.

Don’t bog your jellies down with high salinity levels in your jellyfish aquarium!

The first and biggest problem I see is maintaining water quality–specifically salinity.  The problem seems to be in the hydrometers that are generally purchased to measure the salinity. The plastic hydrometers that are on the market, and even the more costly refractometers need calibration.  Using either one of these instruments right out of the box will yield a variety of readings which is not good when you are trying to establish the salinity level of your aquarium.  Payam left with 20 gallons of my natural ocean water, salinity 33ppt, and when he got home and tested the water with his newly purchased Deep Six Hydrometer, it was reading over 40ppt!!  I knew this was incorrect.  Payam returned it to the store and bought another one.  Same problem.  Then he purchased yet another one! Finally–Getting closer! Third time’s a charm!

Now, I know from personal experience because I have 2 of them myself and each one reads differently. The trick is to calibrate it with a known water source and then simply account for the difference each time you use it.  It’s no big problem to do.  The third one Payam purchased was a bit closer to an actual read and we agreed that he will bring it in for me to calibrate properly soon.  The point is, if you are continually having problems with your jellyfish eating, belling or pulsing, or just not thriving, you should first look to your salinity level.

Moon jellies perform better with a salinity level between 32-33ppt. Don’t worry if you go a bit below that because lower is better than higher. Just don’t alter the salinity level too much at one time but do it gradually over a few days.  And, never add distilled or RO water to your filter box as it will kill your beneficial bacteria, which are a marine (saltwater) species of bacteria and are also affected by salinity & pH.  Also, keep in mind:  depending on your geographic location and evaporation rate, you may need to check your salinity twice a week.

Here in Los Angeles we have very dry air and experience quite a lot of evaporation. But, again, it’s hard to know that if you have an instrument that is inaccurately reading your water.  Try taking your hydrometer to your local hi-end reef / fish store and see if they will calibrate it for you.  What you want to know is how many points off your hydrometer is – either too high or too low– and then just account for that each time you take a salinity reading.  For example, when using my plastic Deep Six hydrometer in a pinch, I know it reads 3 points too low, so I just add 3 points to whatever it is reading.  When I do have a chance to test it against my pricey refractometer, it is consistent with my adjusted plastic hydrometer read.