I don't really understand everything you have said, but a few things:

Yes, 5 drops of R0003,

The returning pink color probably indicates that you are adding the drops too slowly. About 1 drop/sec.

Kelemvor suggested you get your FC up to shock level, perhaps around 20ppm. That means getting it there and KEEPING it there. e.g. When you tested "5 hours later" and it was 7, you needed to bring FC back up to 20. Please let us know if you need more specific instructions on how to do this.

Try putting a vitamin C tablet on the steps and see if it has any effect on the brown stain.