A 'green' saltwater aquarium.

This is a capture of sea creatures collected from rockpools in front of my house in Spain. I changed a gallon of stale water for a gallon of fresh from the sea daily. Crabs, shrimps, sea urchins, hermit crabs, small fishes (in the fore ground) came, stayed for a while then returned to their pools. This could only happen in the 4 winter months as the summer temperatures made the water too warm. Everything, rocks, gravel, sand, sea weed all went carefully back in to the rock pools till the next winter.
I did feed an octopus in a rockpool for several months but that's another blip!

The extras show the rockpools 50m from my house.