See below

Well, what wed do for a Halloween party would be to make a Toxic
Aquarium. Mix orange and blue jello to get a putrid shade of green.
Lifesavers make old tires and you can toss in other junky things for
trash on the bottom of the sea. Something barrel-shaped (root beer
barrels?) for that illegally dumped toxic waste. Float your fish
upside-down on top, and add a plastic skeleton or two. Havent
figured out a good way to put something on the bottom to represent
the sand.