black fins on clarks clownfish

[huff2]

hello can someone help me one of my clarks clowns
has started to get black bottom fins and also tail fins it stared at the very tips of his fin and is making its way through the fin and growing. I have a qt tank that is only been set up for 3 weeks that
i can run copper with but just want to know what it is.
thanks.

 

[kevin2000]

A picture would help ... but its pretty common for clowns to change color as they mature.