painted turtles fighting?

Question
We have two painted turtles sharing a 75 gallon tank.  Recently, one of them has been biting the other's rear foot.  We've had to take them out of the tank to separate them.  I'm assuming they are not getting along, and we're looking into getting a separate set up--is there any other reason they could be doing this?  It has happened three times in the last 2 weeks.  Thank you.

Answer
2 main reasons:

1. Habitat is too small and they cannot avoid confrontations. The rule of thumb is about 10 gallons of water per inch of turtle. A 1/2 filled 75 tank is about 40 gallons, so if your guys total more than 4", the space may be too small.

2. Some turtles are just plain bullies and the only thing I know of to do then is to separate them.

Try http;//www.austinsturtlepage.com for more info on this species.