I have the same problem with my turtle tank...
Every now and then, I mess up and change too much water or clean the filter and do a water change... I don't run bio media, yet. It takes about a week or two for the water quality to get back to normal... The worse thing about it is you can't really do much but wait it out... The more I tried to "fix it" the worse it gets... Extra water changes don't help (I learned that the first time). I also tried to add more black carbon, more filtration, more water movement, but nothing but time helped...
I picked up a few Glade Plugins... You could only smell the tank above it and right next to it a few hours later.
Two weeks later, my water is crystal clear and tank only has a hint of a fish/turtle odor.