Can you charge a tenant for a rust stain in the bathtub?

[Lisa Craig]

Hello!  I have a condo that I rent out in Michigan.  My renters just moved out and they left my condo filthy.  I've been reading up and apparently in Michigan I cannot deduct a cleaning fee from their security deposit.  However, they left some rust stains in the corner of the bathtub (what looks like from a metal can they had there), I've tried CLR, Lime away, bleach, etc. and I cannot get this to come out.  Is there something I can withhold from their security deposit for this type of thing?  Any input is appreciated.  Thank you!!