I came back from vacation and my tank looked similar to yours. I tested and PO4/NO3 were testing zeros with hanna checkers. I did a water change regardless and the next day it was worse. I started reading everything, bought a cheap microscope off amazon. I posted my slide on a thread and it was determined i had prorocentrum dinos with a few ostreopsis strains. I stopped water changes, went 3 days blackout and on day 3 fired up the lights on a lighter 6 hour schedule and it all came back even worse. I started feeding as usual and read that UV light and adding phytoplankton w/ copepods helped several people knock it down. I had a UV in storage and ordered some pods from algae barn with their oceanmagik phyto blend. After using that for two weeks the dinos subsided and the tank is back to normal. I had lost two acros, all my snails and a bubble coral during the battle. Things are doing fine now but i always have my eye on keeping my PO4 at around 0.02 (ULR PO4 checker) and my NO3 at around 5 ish. That seems to be my sweet spot.
My friend that was feeding my tank when this all happened admitted that he missed some feedings and my algae reactor took care of the rest.
