Basically you could take the reading after your tank water and sump water have exchanged. So let's say wait 30 min.

That's interesting, but, my level was 460ppm right from the start. I didn't add anything other than salt. Should a person then lower the Ca?

Walter

Usually when you raise just your alk your calcium level will drop.

well there is two theories on this right now and I haven't decided which one I believe yet :mrgreen:

the first saying that the max rate is achieved at 360ppm so anything higher is a waist, but not a problem so run it where ever you are comfortable.

the other theory is that to high of a concentration actually causes the coral to expend so much energy expelling Ca from its tissue that its growth rate is hindered.

so if you are running high Ca and getting lousy growth maybe try dropping it to 400 and seeing what happens.

Steve