This is a question we get all the time when folks see a jellyfish Tumbler Tank. It looks like a traditional square or rectangular aquarium, but it has some specific modifications inside it that make it safe for jellyfish.
Back in the 1960’s the plankton kreisel (German word meaning, “to spin”) was crafted to hold all sorts of planktonic animals because it was evident they could not survive in a normal aquarium. They needed a current inside the tank to assist them to swim or bell, otherwise they just laid on the bottom of the tank. A piece of acrylic was formed into a circle and placed inside a square aquarium. Then a small stream of water by way of spray bars was introduced along the interior of the circle. This created what is termed, laminar flow. The spray bars created a false current by spinning the water around the interior of the circle. Think of a whirlpool effect—the water movement going around and around kept the planktonic animals up in the water column and not resting on the bottom of the tank. It was revolutionary!
That was over 45 years ago! Since that time many new jellyfish tank designs have emerged and each one has its benefits. There are true kreisels, like originally mentioned, a true circle inside of a square aquarium and there are pseudo kreisels. Pseudo kreisels include those plankton kreisels that are modifications of the original and include Stretch kreisels where the tank is longer than it is tall and these can be either Horizontal Stretch kreisels or Vertical Stretch kreisels, and there are Cylinder and Half Cylinder tanks, as well as, Modified Tumbler Boxes.
The important thing to know are the key features that make a jellyfish tank safe for jelly keeping. The flow needs to be consistent and even and the drain or overflow needs to be protected.
Because jellyfish move with the flow of water, wherever the water flows, so will the jellies. So, if the water flows into the tank, it must flow out by way of a drain. This drain must be protected or guarded otherwise the jellies will go down the drain. You need a tank that can properly create a nice even flow for the jellies to swim or bell, and a safe guarded drain so they don’t go down it. Two very simple, but important requirements for a jellyfish tank.
So, what is up with the Jellyfish Tumbler Tank? It isn’t round or cylindrical?
No, it isn’t, but it doesn’t have to be as long as all the bases are covered—even and consistent flow and a protected drain. It may look simple, but the inner workings of a Tumbler style jellyfish tank are just as intricate and defined as with a standard kreisel tank. The spray bars are well defined in two places. The drain is protected by a screen and a spray bar that gently moves the jellies away if they get near. The Tumbler tank creates a gentle turnover of the water column so the jellies can bell freely without being forced around and around like on a merry go round.