How many gallons for these fish?

[ismailshah]

Hey guys,

I’m planning to get a nano reef tank but not sure which size tank to get for the following:

2 clownfish
1 red fire shrimp
1 hermit crab
(Potentially a barnacle blemmy too)

I was thinking 20g but not 100% sure.. any ideas?

 

[Gumbies R Us]

20g!