I have a mixed reef tank. Fish, lps, ricordia, and zoas. The past 4 weeks my lps have been struggling. Duncans are shrinking and zoas are only half open. I tested my water and had my lfs teat as well. 78 degrees. Ammonia and nitrites are zero. Nitrates are at 8 and phosphates are almost unreadable. But calcium is over 600 and alk is 8. I have a ton of cyanobacteria on the bed I'm treating with chemiclean. Corals were struggling prior to chemiclean. Filtration is filter sock (changed weekly), chemipure elite (removed a week ago when started dosing chemiclean) and a ton of cheato in the fuge. The fuge is packed with cheato and I need to give it a good pruning. I have done a 50% water change over the past 2 weeks. I dose with sea blocks so I think that is why my calcium is so high. Would the high calcium and alk negatively impact my corals? Or the cheato pulling too many nutrients from the water? But if that is the case why do I have cyano? Not sure what to do.