When is it ok to....

[SbCaes]

hey guys I've always wanted a school of firefish. But I'm aware that in our nanos's they can only be kept singly or in a pair.

 

But there is always that exemption that "should be kept singly or in a pair, unless tank is big enough"

 

my question is ... how big is big enough?

 

Do you think a 36x18x21 tank would suffice? equivalent footprint to a 40 breeder just 5 inches taller?

 

Or what is big enough????