Proper nitrate level for Anemones or Coral

Question
Hi-  I have an 120 gallon tank that has been set-up for 6 months.  It is stocked w/ clowns, anemones, 1 tang, etc.  My question is for the levels needed for Anemones and/or Coral.  For the last month it's moved from 0 to between 20 & 30.  What is the proper level for an established tank?  I keep trying for 0 but am now wondering if I am shooting for the moon.  All other levels are perfect, I just need a reality check here.  Thanks for your time.

Answer
nitrates are tough to control. there are types of media to absorb nitrates but there is a diagram for a nitrate remover on about.com, click on hobbies, click on saltwater aquariums and you will find many answers. levels for corals should be as close to zero as possible. they will survive 10 to 20 depending on species. anemones up to 30.