[Coral-List] Water quality parameters?

[Jade Maggs]

I work in a public aquarium and I look after a coral exhibit which is predominantly soft corals. The total volume is around 20 cubes half of which is the sump and Rk2 skimmer. The configuration is semi-open, with make up water from the sea being added continuously. The problem I have is that our incoming water has ammonia up to around 0.2 mg/l but more like 0.1 mg/l. The water also passes through a sand filter between sump and exhibit and readings have indicated the sand filter resulting in a slight drop in ammonia and nitrite and a rise in nitrates from 3.5 to 4.5 mg/l. Are these values too high, just acceptable or completely acceptable. The nitrite is around 0.024 mg/l. I know everything should be around 0 mg/l, but how critical are my values. 

My solution is to turn the make-up to a trickle and pile in the live rock and create a refugium in the sump. My problem then is to chill the water as the make-up keeps it within an acceptable range. 

Any help advice would be much appreciated.
Jade Maggs
Aquarist
uShaka Marine World
083 515 1079