- Fine sand- I have found that using a very fine and soft sand in many jellyfish aquariums is good. Rougher sands such as crushed coral can pose a threat, as the jellyfish may scrape into it from time to time. Rougher sands also have more space to build up decaying food. That will need to be siphoned out, which can be a risk to jellyfish. Beach sand often works well, but many pet stores sell bags of fine white beach sand as well. I wouldn't use sands that aren't from the ocean. Sand is good in aquariums for Upside Down jellyfish, Lagoon jellyfish, and Cannonball jellyfish. Kreisels and sand don't mix as the flow in kreisels will stir up the sand and it will never settle. That would be the equivalent of a sandstorm to your jellyfish.
- Glass pebbles with or without rock- Glass pebbles can add a cool colors to your tank, and make the bottoms look a little less bare. Rock can often go under the pebbles to help with biological filtration. This combo works well in cylindrical jellyfish aquariums. I have found that moons seem to be okay with this the most. Upside down jellyfish can tolerate it, but must be a few times larger that the pebbles or they will get sucked under or stuck between the gaps in pebbles. I tried small Atlantic Sea Nettles and had some success as well. Unfortunately the large gaps do allow for build up of decaying material. It is good to remove the jellyfish and do a major siphoning every few months.
- Bubble wrap?- A very interesting article by the Monterrey Bay Aquarium, explained that they were able to rear Crown Jellies(Cephea cephea) by using bubble wrap. The article explains that the jellyfish were making contact with the edges of their kreisel tanks often, and perishing because of it. At some point in time they discovered that the jellyfish were repelled by bubble wrap. After coating the edges of the tank, the issue was resolved.