A lot of the information I have read says less than 20ppm - so 5 to 10 should be OK. If your nitrates start to get high you may need to do more frequent water changes.
Brewski
Whoa! Be careful - you won't really notice any problems but your corals and fish - depending on tank type will suffer over time (reduced growth). Try to bring it down a bit.
Brewski
emperor 400 is the filtration. Fish really look good and happy though even my hermit crabs are running all around! Although two did die but 4 months and no fish problems!