You can't. Keeping jellyfish requires preparing special artificial seawater to simulate ocean currents. The living environment of cold boiled water with salt is very different from that of jellyfish, so cold boiled water with salt can't raise jellyfish. Attention should be paid to raising jellyfish. There must be no bubbles in the water, because if the jellyfish accidentally sucks the bubbles into the jellyfish wings, they will not be discharged. When bubbles accumulate to a certain amount, the wings of jellyfish will be punctured by bubbles, leading to the death of jellyfish.