Despite the fact that jellyfish are 90% water, many other predators still require to consume the jellyfish in order to gain it's nutritional value. Leather back sea turtles main diet is mostly jellyfish, including the purple striped jellyfish. Having delicate jaws, the sea turtle is restricted to only eating the soft bodies of jellyfish. Leatherback turtles weigh up to 1,500-2,000 pounds, in order to achieve this weight, they need to consumer about 440 pounds of jellyfish everyday. They will also dive more than 1,000 meters so the leatherback turtles can reach the jellyfish that other predators can't get to.
Tuna are extremely fast hunters that require lots of energy in order to survive and hunt some more. They have very quick metabolism so the tuna needs to eat plenty of the little jellies. In order to make all the chasing and hunting worth the tunas time, they would have to consume about 31 pounds of jelly fish per day. The purple striped jelly fish though are not more desirable as the other jelly fish like the comb jelly.
Sunfish's (or the Mola mola) average weight sums up to a hefty 2,000 pounds, but some have been reported to reaching weights of 5,000 pounds. There is no exact number of consumption for the Sunfish, it eats constantly, the more it chases, the more it eats. The sunfish would arise from the deep cold depths of the ocean to feast on the little jellies and other sources of food (such as salps, squids, and crustacean) Upon reaching the surface, the sunfish also warms up, and is clean of parasites from different fish.
As weird as it may seem, butterfish not only eat jellyfish, but use them as a protective shield against predators. The butter fish is unable to eat the jelly fish as whole, so it bites off chunks of the jellyfish and begins to grow an immunity to it's poison, allowing it to swim among the jellyfish's stinging tentacles. It's not a very generous relationship between the two. (Right image: baby butterfish hiding in the jellies tentacles.