The tank simulator is very customizable for this game's era. The player can select from a large number of backdrops and tank ornaments for the fish to swim between. The user can also import their own images to use as tank ornaments. "El-Fish" includes a fractal based plant generator for creating unique aquarium plants. There are several "moving objects" that can be added to the tanks which the fish will react to, such as a cat paw, fibcrab, and a small plastic scuba diver. The user can also procedurally generate background music for their tank using an in-game composer, or choose a separate MIDI music file to be played for each virtual aquarium, and feed the fish.