I too damaged the interior of my cedar tub and have been looking for information on how to repair it. Seems my damage resulted from over use of bromine when my UV system was down. Anyway I found this today and while I have not tried it yet I am going to give it a shot this weekend.
https://www.cedartubs.com/blogger/tickets/af1c1eb4a13736d8431a107b557fed1bCedar-Tub-General-Care-Manual-Rev-13.pdf
I see your post is well over a year old so if you have any pointers since I would appreciate it.
Thanks
