I am back to having tank issues that I can't explain. This is the third time in the last year and a half with the exact same symptoms. Let me know if you have any thoughts or ideas. Here are my parameters and some details. PO4 - .02 - .04 Nitrate - 5 - 10 with the exception of the spike described below Alk - 8.2 - 8.5 and stable for 6 months Ca - 460 - 480 Mg - 1460 SG - 1.025 Here are the first symptoms that show up every time. - Some coralline algae turns white and some dies off. There is also new coralline growth in other parts of the tank at the same time. - Sunset Monitpora turns a greyish color - PC Rainbow starts to show STN - Miami Hurricane Chalice turns a greyish color - Many other acros and montis begin to grey out and/or lose tissue a couple weeks after the first symptoms appear I have taken hundreds of macro photos and dipped many of the corals without seeing any pests. It also appears that this is a slow process of the coral wasting away and not pest related. The last two times this happened I had an increase in nitrates prior to the issue. Back in June I was not keeping an eye on nitrates and they had climbed to 50 when the issue began. About a month ago I accidentally knocked the plug out of my skimmer cup for a week and nitrates rose to 20. Both times I did water changes and lowered the nitrates to the normal range within a couple weeks. I also noticed a very quick degradation of par from my t5 retrofits after 6 months and this issue has always happened when my bulbs were 6 months old. The par for where my WD (which is unaffected) sits decreased from 350 in early November to 250 in mid December. I am thinking maybe the lower par combined with the nitrate issue may be the cause, but I really have no idea. Here is a series of photos showing how it progresses in acros. 11/4/17 pink cadillac 10417 by Big Jim, on Flickr 11/18/17 pink cadillac 111817 by Big Jim, on Flickr 12/3/17 and I am thinking I am the master of acros pink cadillac 120317 by Big Jim, on Flickr 12/12/17 and some white patches are appearing pink cadillac 121217 by Big Jim, on Flickr 12/24/17 and the white areas are growing Pink Cadillac 122417 by Big Jim, on Flickr I don't have the most recent picture but it is even worse and now it looks like it is losing some tissue. I tried a CoralRx dip as a last resort yesterday. Maybe a bacterial infection that comes back under high nitrates and/or lower par conditions? Please let me know if you see anything I am missing. I am probably going to try another ICP test as well.