I am new to turtle keeping. I have a pond about 2500 gallons with Koi.
I have two adult western painted turtles. They actually don't mess with the Koi fish. None of the fish are smaller then the turtles. My question is am I safe in keeping the turtles throughout the winter in my pond. I live in Ohio and keep a heater so that my pond does not completly freeze over.

They should be ok. I think the Western subspecies is less cold tolerant than the Eastern subspecies though. They both should survive in a pond down to freezing as long as they don't actually freeze, and there's a hole in the ice. These pages on my site may be of some help for overwintering your turtles.

http://www.fishpondinfo.com/turtles/turpond.htm
http://www.fishpondinfo.com/winter.htm

Thanks for the info. I was wondering about adding something to the bottom so that they can nest or hibernate comfortably.
I really like the turtles and was wondering if i could add one to two more before doing harm. If I do should I stick with painted or could I mix with red ear?

Since your new to keeping the turtles in your pond, I would at least see how they do over their first winter. You could put a red-eared slider in with the two painteds but RES's do grow larger and may be more bossy to the painteds. Turtles sometimes burrow into dirt in the bottom of natural ponds. In your pond, you probably don't want dirt down there but they might use some sand. Leave some leaves on the bottom for them in the fall. Hiding under some leaves should be enough protection for them. Adding dirt, sand, etc. just dirties the pond. If they burrow into that, they may also not get enough oxygen exchange through the water. In the winter, they get some oxygen through skin-like areas in their mouth and anus. I just discovered that. See http://www.tortoisereserve.org/Sundry/Hibernate_Body2.html