I agree that the roselines are probably getting ready to spawn.
my group of 4 is a little older than yours but they still have the yellow on the fins but the fins are not elongated. they can be seen in this full tank shot of my 65g:
probably the change to RO water has caused this change.
often times it mimicks the 'wet season' in wild fish and can a trigger this change.
keep us posted!

my group of 4 is a little older than yours but they still have the yellow on the fins but the fins are not elongated. they can be seen in this full tank shot of my 65g:
probably the change to RO water has caused this change.
often times it mimicks the 'wet season' in wild fish and can a trigger this change.
keep us posted!
