It may well be that the snake is preparing for hibernation and is therefore off feed.
My lycodonomorphus (many years ago) fed well on goldfish and guppies. He seemed to prefer to fish while submerged and anchored to tree roots below the surface.
Water temps where about 72F and air 80F with a sunning lamp at around 95F.
The setup was a very large tank with approx. 8" of water with under-gravel filter, branches rising from the water and several islands set at random about the tank.
MY MISTAKE was that I had English ivy growing profusely throughout the tank and water (rooting beautifully and always green). Turns out the stuff is toxic! Might have been alright had I not allowed it to fill so much of the water volume.
Michael