If a jellyfish is floating on top of the water in your aquarium, first ensure that there isn't anything in the tank that could be causing the jellyfish to float. If there are no objects in the tank, then it is possible that the jellyfish is dead or injured and should be removed and replaced. To remove a jellyfish from the top of the water:
1. In shallow water surrounded by rocks or sand, gently scoop up the jellyfish with a net. If necessary, use a pot or other container to position it so that it floats horizontally in front of you.
2. Gently pour some dishwashing liquid over the jellyfish, being careful not to splash it around or put too much pressure on it.
3. Once the jellyfish has been covered with liquid, drop it into the aquarium. It will sink to the bottom and release its stench. Repeat this procedure for any additional Jellyfish floating on top of