I too never go below 1.023, but I know AA keeps their tanks at around 1.020 and the inverts there appear to be healthy.
As for treating for ich, I think you're outta luck.... unless you can catch them and treat in another tank.
I'm in a similar situation. I made a stupid mistake and transferred the parasite into my tank back in mid December. Knowing It'd be near impossible to catch all 11 fish, I've just been keeping an eye on the fish. Most have seemed to develop an imunity (only powder blue occasionally shows a few specs every wek or so), but I know ridding my tank of the parasite is near impossible and someday when I've got the time, I might try to fish them out.
Cleaner type shrimp will help.