Oh my god! I am so sorry for your bath tub cleaning.
I had no idea it could be problem.
That was Lush bath melt used to drop in bath tub.
Lush is huge nature friendly cosmetic company from UK.
I usually use it in my bath tub and hotel bath tub.
So I thought it is ok to yours either.
Again, I am so sorry.
If I knew it could be bad for your tub, I would not use it.