Hey everyone. I've had a mixed nano reef set up for about 6 months. It is a waterbox 20 cube with pretty minimal stocking. Right now, it's just a pair of clownfish, a red mythrax crab, some hermit crabs, and a few snails. I've had some mixed success so far but things seem to be falling apart. I started with a pavona, a montipora digi, two montipora caps, a stylopora, an Avatar chalice coral, two rasta zoanthid colonies, a red unnamed zoanthid colony, two gsp frags, a candycane coral, and a bubble tipped anemone. Some of the corals seemed to be growing well until some of them randomly died back or disappeared. The stylopora and monti caps died completely and the pavona lost most of its tissue when I moved the tank last month. The other corals have been declining since. The chalice has browned out. The zoas had explosive growth up until today, but all 10 heads of the rasta just disappeared today without a trace. The montipora digi was growing quite well but now is missing tissue on an entire branch. That started on Friday. The gsp and clove polyps are growing explosively and seem fine, and up until today the anemone was getting quite big, but is now shrunken back and looks sort of sad. This also started on Friday. Why is everything declining? My nitrates are a bit high (20 ppm) and have been as high as 80 before from overfeeding while on vacation, but the corals have been doing find for a few weeks since then and I've been told by local hobbyists that this isn't likely the cause of death but could be why the chalice is browning out. Ammonia and Nitrites are 0, salinity is 35, ph has never been below 7.8 or above 8.1, temperature has been between 75-79 F the last few months since I had an AC failure, calcium has been around 400ppm and alkalinity has been 8-9dkh. I don't have magnesium or phosphates test kits. I do weekly water changes but did some more dramatic changes (10% per day for a week) recently because the nitrates got high while I was on vacation. I don't see any visible pests and I dipped all the corals before introduction to the tank with coral RX and hyposalinity and inspected them. I've followed all the information online and feel like I'm quite knowledgeable on paper, but I just haven't been having success.