20% water changes have been a huge help for my jelly's well-being.
When mixing your saltwater with RO/DI,
1) ALWAYS use a submersible heater and a low speed pump to circulate the water while the salt evaporates. Heat the water to 75 degrees.
2) Never use an aerator/bubbler while mixing. This seemed like a great idea, but it seemed to deplete/evaporate minerals that the jellies need.
3) Add salt slowly and don't mix the water for more than two hours. This also depletes or evaporates essential elements in the water.
4) After two hours of mixing, your water should be crystal clear. Test your salinity. I've had the most success at 30ppt and use a refractometer with calibration solution.
5) Test your tank's PH and the PH of your new water before introducing it into the tank. If your new water mix's PH isn't at 8.3, try adding a teaspoon of Seachem Marine Buffer to the mix, which will safely raise it to 8.3.
Pic of my jellies:
https://drive.google.com/file/d/0BwVbT6 ... p=drivesdk