Removing bathtub tread
The manufacturer recommends sand paper. Solvents are ineffective. Perhaps in a sealed enviroment solvents might work, but everything evaporates too quickly. I have gotten the stuff off and here is how.

Sand with 36 grit paper on a belt sander.

Patches may remain if the tub does not have a flat bottom. If so, use large grit paper by hand to sand off patches.

36 grit paper WILL leave the surface dull, and over sanding can cause series damage. A razor proves effective when submerged in goof off. But only for small patches. You will need to refinish the surface no matter what. ESPECIALLY if you use a razor.

If your unlucky enough to need to do this, I am truly sorry. There is no easy way. Give up hope.