In order to save the jellies, I converted the 30 gallon into a temporary cannonball jellyfish tank. I removed all the live rock, and anything that had sharp edges. The result was a sand bed and some macro algae. I let the jellies go into the tank. After watching them for a while, I assumed it was safe to add a small hang-on in tank filter. The next morning I woke up to find a jellyfish stuck to the filter. Over time its flesh seeped into the filter and formed into the shape of the protective grid. The jellyfish was dead by the time I woke up, but after spending a good 5 minutes working it out of the filter, I found myself with a handful of jellyfish chunks. I decided that I would need better way of filtering the tank.
I took a cooler, and attached a flexible hose to the drain at the bottom. All of the live rock, hermit crabs, snails etc. were placed inside the cooler. Water was then added to fill it up. I took a small fountain pump and used it to pump water into the cooler, and let water drain out of the cooler at the same rate. In a sense, I built a sort of reverse sump. Its pretty low grade, but seems to get the job done. Inside the sump i have three air hoses running, and the internal hang on filter.