well, with th nitrates (unlike nitrite and ammonia, where any ammount is toxic) there is a bit of leeway. you can have nitrates as high as 40 ppm
. i would say with not that many bad effects. 10 or less is ideal. but for corals even 10 can cause big problems with the more fragile ones.
concerning the PH
around 8.2 is good. some like it a little higher in their reef tanks though, 8.4 i think is the highest i have ever seen anyone wanting it to be.
and for the Alk
. and calcium, the Alk
. should be around 2-4 and the calcium about 450, that would give you some nice corraline growth (especially with good lights)