Ok so I have never posted on here before but I just signed up bc I need help. I have a fluval evo 13.5 with an AI Prime. Starting around december I saw a little tissue necrosis on the bottom of my pocillopora, and I thought it was just bc it was not getting enough light, but within the next few months all of my SPS have died from RTN. Now even my LPS are dying, two of my acans have receded a ton so there is a lot of skeleton showing, and my leptastrea, which had been doing great until a few weeks ago, has a few spots of dead tissue. A few days ago, my firefish (my only fish) died as well, even though my nitrates seem to be undetectable, no nitrites or chlorine etc. Now one of my flower nems has completely detached and is curled up in a ball at the bottom of the tank. Does anyone know what could be happening? I for sure have had some calcium/alk unstability, I had never even tested for them for the first year and a half with this tank doing fine, then I got a doser and started testing and dosing in january. I messed up and way overdosed calcium which brought my alkalinity down a lot, but they both got within good range a few months ago (I thought). However, I started out with API test kits and just a week ago bought the Red Sea pack for Alk, Cal and Mg and apparently my calcium and alkalinity were much higher than the API tests showed. Right now Alk is 9.5 dKH and Calcium 545 ppm. I have decreased my calcium dose, but still, this wouldn't cause my fish to die, right? Is there some parameter that I could be missing? I have been using a basic tetra 6 in 1 test kit for nitrate, nitrite etc and now I ordered a salifert nitrate test to make sure. I also ordered a phosphate test. I have also been dealing with dinos, and started dosing <1 ml of Vibrant 3 weeks ago, but it has only gotten worse. Should I stop dosing Vibrant, or get rid of my fuge, or is there anything else that could be causing this?