like circle round? or if i put a dot in the middle of the circle and its gonna have 4 right angles round? im gonna say no.
this is my opinion
cause its gonna be only 5 ft at its wides
silvers get at least 30inch+
it wont give him enough swimming room
since its round the only place he can cruise is in the middle
if it was a a 5ft by 5ft rectangle pond you can measure it from mold to molding and it gonna be 5 ft. but if you measure certain parts of a circle pond some parts are gonna be smaller.
which might make certain parts of the pond more difficult for him to turn around because its at a curver rather than straight.
heres my little diagram.

hope this helps