well...depending on what your aspirations are, you can create a pico reef with anything that's as small as 1 gallon. pico reefs are defined as being 3 gallon's or less while nano reefs are 3.1 gallons up to 33 gallons.
these guys are so simple as you essentially just do a 75% water change once a week on a pico. you just need to have a proper lighting and heating, which are both easy as well. you use a small air pump and air stone to create circulation. a pico isn't really suitable for any fish...you need at least 5 gallons for the smallest goby's, but you can put all sorts of corals, crustaceans (crabs, shrimp) and invertebrates like snails and starfish.
for pico's, a lot of people use a 2 gallon jars by Anchor Hocking called the Heritage Hill. NOT the Montana...glass is not clear. I know...bought one. that Heritage Hill jar isn't really available anymore (at least not in Canada)...but it gives you an idea of just how simple they need to be. if you check out angelfins.ca, take a look under their rimless tanks and you'll see options from 1 gallon and up. choose starfire glass if you can afford it's premium. it's almost crystal clear and has little green tint like non-starfire aquarium glass has.
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