With the cover still wet .....
Tried the Karcher, stains still there;
Tried the vinegar and water stains still there;
Tried straight vinegar stains still there;
Tried the oxy action stains still there;
With the cover still wet .....
Tried the bleach 20% mixed with water stains still there;
Tried the bleach straight ... in about 10 minutes the cover was like new.
Threw the cover in the swimming pool to rinse, most difficult part was trying to keep it fully submerged.