These are the sand filtration units for the main oceanarium at the Aquarium, there are four in total... The water is pumped from the sea and through a natural filter, the shingle beach the aquarium is suitated next to and into these cylinders filled with sand... The water goes through them at over 15 psi... The filtered water is then sent through four different pipes (one for each) to different location in the main tank... This system is over-engineered, i.e. large parts of the system are turned off the majority of the time and it is not required to run anything near maximum capacity...
