My RES's name is Turtle. Turtle has been acting weird for a good half of a year when basking.
The strange behavior is when he's on his basking platform, he would shrink his head into his shell and keep moving backwards with his legs and arms (until eventually dropping back into the water).
He keeps going up and down on the platform doing this and never really basks for a long time by himself.
Because of this, I've put him in a container to bask for a couple of hours everyday (he is fine in the container and sticks his legs and head out without moving, sometimes taking a nap).
Currently it is almost spring, and noticed this issue in the fall about 5-6 months ago (North Eastern US).
I've brought him to a vet and the vet found nothing wrong (blood test + xrays).
The vet could not explain this behavior.
He was put on a course of antibiotics about a month ago.
Turtle is ~20 years old, and is very lively still.
Before the antibiotics he seemed fatigue (while still eating and pooping regularly), now there are no remaining symptoms of anything wrong except he still dislikes my basking platform.
Turtle:
20 Years old
Male
~8 inches in length
Feeding him every other day, a little mix of the following:
romaine lettuce, bok choy, other green leaf veggies
pellets (reptomin, mazuri, and 1 other) ,
calcium supplement (once a week),
Treats:
dried baby shrimp,
dried crickets,
dried mealworms,
Setup:
100 gallon stock tank filled about 75-80 gallons
Fluval FX6
PVC pipe created dock + a water resistant tile from Home Depot
UVB 5.0 26 Watt (Exo-terra), and a Heat Lamp ~12 hours a day
Surface Temperature varies between 85-95 (~80 ish when it gets wet)
Water heater in the winter for a temperature ~78-80
Aerator constantly running
15-25% water change weekly (sometimes a 50-65% water change)