Reala 500D does not have a green base - it's orange like other films. It could be that something has affected the film, or it could be your ECN-2 processing. Reala 500D was introduced in 2001 and discontinued in 2011, if that is what you have it might not be that old, but who knows how it was kept.

I had a long thread on here a while back about ECN2 processing that might be helpful. I did find that certain tweaks to the formula helped me with small tank processing.