I have been reef-keeping for almost 3 years and my zoo's have me perplexed. I have a 45 gallon show tank with a 15gallon refugium. All the basics are 0 (ammonia, nitrate, nitrite), my pH is 8.3, alk in good range, temp=82, medium current, Ca2+ is 350, phosphates=0. I drip kalk everyother night. Recently my zoo's haven't been opening up likr they used to. They only open about half way, and that's it. They don't appear to be dying or infected with anything that is visible. All other corals and clam are doing fantastic, including my LTA. Fish are healthy and have a great appitite, including a new Anthelia. The zoo's are spread randomly throughout the tank which aliminates any lighting or current problems. Skimmer is going full blast but isn't pulling anything off. I even tried to run some carbon to see if that might take out any impurities. I have done a few water changes, but to no avail. I have also inspected them for any parasitic infections but don't see any. Thought maybe it was an iodine issue, so I added iodine. Nothing seems to help. They always look the same. No more than a month ago they were reproducing at about a rate of 1 polylp=7/month. I am out of ideas. What could be affecting them but nothing else? Do they have a sensitivity to something that other corals might not have? Any suggestions wouls be helpful.

Thanks,
Matt