You probzsbly need more kalk, check you AM pH for the system. You will usually see your average moring system pH drop around 0.1 oH units every morning (if it is usually 8.1, and it suddenly starts being 8.0...) once the media begins to reach depletion. Lots of the stuff left over is some of the trash in the original Kalk powder (misc quartz, mud, calcium carbonates, etc) that will not dissolve in water at 7.0-7.4 pH. If you haven't been keeping up with your normal am pH's, then just go ahead and clean out the reactor, replenish the media, and start it up again. Getting back to max levels in the system may still take a few weeks, but it will slowly climb back to your max supersaturation quotient for your system within a reasonable period of time. You didn't mention your populations of corals or an estimate of their sizes, a photo would be good, but unless your system has a large
stony coral population, it is most likely that your media is exhausted.
HTH
