Thanks peoples. I didn't know that magnesium plays a role. So let me ask you this, should I let my reactor run wide open and shut off CO2 until it levels out. How do I bring the DKH down or control it. It seems that every time I run the reactor my DKH skyrises. I decrease bubbles and change the centervalue higher to get less burn. By calcium is at 460 - the Ph is 8.4, but DKH is rising. The only way I get it back down is a huge water change. I am doing something wrong here. If I can correct that I will have accomplished atleast something this year in regard to actually keeping the hard corals. They look great like I said - when I change major water. I'll check that magnesium now. Thanks though. You are all helpful