Do you have two lapped sides or only one. I know when I got my zulu (first natural) I was hesitant to do anything on the surface. But with some reading and new found courage, I started to experiment with it. Best thing I did!
I recommend to take one side and lapp it with the DMT 325, rinse and try with water. If that doesn't do anything, try with a little light slurry raised with the DMT and dilute every 15-20 laps to water. Test on arm hair or HHT test, or whatever you're using, and if it improves, go to the smooth side and do some more laps on that and try the shave test.
All naturals vary from one to another it's up to the user to find out how to get the most on that specific stone. Keep reading, experiment and don't give up. Don't get another stone until you have tried everything with that one. It's my best advice to you! Double O
One sided but I think the other side is darn close to being flat. So it should be able to be lapped and usable.