Despite what some conspiracy theorists might shout at you, tap water is generally safe to drink for humans. For jellyfish, on the other hand, it might as well be poison.
Tap water contains small amounts of metals and minerals that you and I can hardly notice when we drink from the sink, but even in small concentrations, these elements can seriously disrupt a small jelly’s bodily functions and cause them to shrivel and stop belling. This is why we insist that whenever you add saltwater to your tank, whether you’re filling it for the first time or performing a routine water change, you ALWAYS mix the salt with either reverse osmosis (RO)water or distilled water, and NEVER use water from the tap, no matter how nice your filter pitcher might be.
Same goes for bringing your salinity down with freshwater: ONLY use RO or distilled when adding fresh water to your system.
*** Side note: bottled water is not always distilled water. Your jellies don’t drink Dasani! Jugs of distilled water are available at most grocery stores, but beware as there will be various types of water. Be sure it is labeled only as “Distilled Water” and not “Spring Water,” “Purified Water,” “Mineral Water,” “Alkaline Water,” or anything else. ***
Additionally, if your system maintenance requires filters to be rinsed periodically, it is best to do so with old saltwater taken from your system during a water change, rather than just running it under the sink. Your tank’s beneficial bacteria don’t care much for tap water either, and you certainly don’t want to make them unhappy.
The same rule applies with your algae scrubbers and any other items you might rinse and stick back in your tank. ALWAYS give them a quick dunk in some old salt water or some RO/distilled water and allow them to air dry before you place them back in your system. Your jellies will thank you!
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.
…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!!!