Heavy noisy power steering

[Andy Jones]

My daughters 2008 1.2 fiesta 74k miles, power steering has recently become very heavy and the pump sounds noisy especially when stationary and trying to turn the wheel when at parking speed, I have checked and can see no obvious leaks from the system although the fluid was a little low, and very dark. I have topped the fluid up but does not seem to have made any difference, I am thinking the power steering pump is on the way out?, or could it be just a simple case of changing the fluid? If you increase the engine revs at stationary, to 2.5k the steering becomes easier but the pump becomes very noisy, belt appears to be ok, but does have a bit of play in it , but not sure how tight it should be, any advice would be appreciated thanks Andy