If the tank is a 20, 30 gallon, and you provide enough plants for the fry to hide in, the strongest and smartest will survive, 
(the tank; is; a 20, 30 gallon) (you; provide; enough plants) (the strongest and smartest; will survive; )
the tank you the strongest and smartest
is provide will survive
a 20, 30 gallon
enough plants