what is your Ph at use a calibrated Ph probe Clowns are suseptible to low Ph and does not take much. 1.0 of a drop in Ph can kill a clown if you don't catch it. You could have brooklynella disease in your tank manly clowns get it it may transfer I don't know though, google it. I did a google and it can transfer to other fish similer to Ick. heres a link to some information:

http://saltaquarium.about.com/od/ich...brooklynel.htm

I added a carpet nem on the weekend and the shrimp don't go on it.

I hope this helps.
Bill