Can I use clr in a lined toilet tank?

Most liners are polymeric substances, poly propylene or poly styrene. They should not be affected by CLR. However, find a dry area of the liner and use a Qtip to apply some CLR. Let it stay wet and then look at the material. If it shows no softening or melting, you should be able to use it. Make sure to follow the directions on the CLR.

Yes but tell why, is it rusty looking?