as u can see i have one large finger leather on the lower right side....
i have not noted any slowing in growth or coral overall health due to having a large leather in my tank....
i do run carbon in my 180G tank i run 2 bags of chemi-pure carbon in the sump and i change them every 4 weeks
im not a big water change person either i do about 30gallons every 6+ weeks
so u can keep leathers in an sps tank....
the reason they dont exist together in the wild is geographical and sps like very clean water while softies prefer dirtier water.... this being said they can both live in the same tank but usually the softies do a lil poorper in an sps tank due to the very clean water and the high light and flow.... softies like softer light dirtier water and less flow ... my leather has shed and its never harmed a single sps coral in my tank....
IMO not keeping softies and sps together is an old myth that should be busted by myth busters lol