We have had an outbreak of Dinoflagellates...which we had originally thought was just diatom (fairly new reef, 1.5 months old). TL;DR don't over feed your new reef!!! (I know better too, that's the worst part ) First misdiagnosis lead us to Vibrant to attempt to control the alleged diatom, along with starvation. This was not a good idea! I can't say for certain that it was the cause, but within a few days of the first dose of Vibrant, our Chaeto started to dissolve, it became soft and small bits broke off from any agitation, we discovered this yesterday afternoon and promptly removed it. Another warning sign that it was dino, was our clean-up crew was not eating the stuff...this should have been my red flag! However, even after being part of the hobby since childhood, I had never encountered dinoflagellates until now. Second misdiagnosis...I figured with the structure of the algae, we had a case of brown hair algae, no big deal! I went to scrubbing rocks with a toothbrush, scraped glass clean with a razor, and then performed a WC removing as much of the dislodged substance as possible. We replaced 4 gallons out of a total volume of approximately 15 gallons. We use Tropic Marin salt and RODI from a local aquaculture, unfortunately, my TDS meter had dead batteries, so that will be remedied today. After all was said and done, I changed our lighting schedule, shortening the time from 10 hours to 6, and using only 0% color from the Kessil A360WEs. Then I started reading and researching to see if there was any other steps we could take in the meantime...this is when I discovered my mistake. I believe I have now successfully identified the substance as dinoflagellates and have begun dosing 1.5mL of 3% H2O2 (store bought Hydrogen Peroxide). I have dosed once last night into my surface skimmer, pre-HOB filter, and again this morning. I have also started a 3-day blackout starting this morning to run until Sunday morning where I will resume with a shortened lighting schedule using 0% color only, ramping up to 40% intensity at the max. We also intend to feed live copepods and phytoplankton before our departure, can't starve the fish! I intend to continue a morning and evening dose of 1.5mL 3% H2O2 for the duration of the 3-day blackout. Current parameters: Salinity: 1.026 pH: 8.2 Ammonia: 0 Nitrite: 0 Nitrate 0 Calcium: 500 (I have been slowly reducing this, be careful with PurpleUp!) dkH: 10 Phosphate: <0.25 (time to invest in that Hanna checker...) Inhabitants: Red Scooter not-Blenny Springer's Damsel Trochus Cerith Nassarius Blue-legs Euphyllia (Hammer) Euphyllia (Torch) Ricordea Yuma Ricordea Florida Zoanthids (including Zoanthus Gigantus) Acanthastrea Platygyra Blastomussa Lobophyllia Montipora Capricornus Equipment: 20 Gallon Long AGA AQ70 HOB (2) Hydor Koralia Nano Hydor 100w Heater (2) Kessil A360WE w/ controller Now the big scary part, we are leaving town on Sunday for a week of vacation outside of the country...time to teach my folks(the temporary house/cat/reef keepers) to not only take care of morning/evening RODI top-off, but to also dose the correct amount of H2O2. I am planning on having them only dose H2O2 once per day during our leave. This post is mostly for me to keep a diary of the battle with this devastating pest algae, however, all comments/suggestions/fighting words will be accepted joyfully! Please lend me your experience in dealing with this miserable pest! First photo is before the outbreak became serious. Second pic is post scrub/scrape before the WC, I was in too much of a hurry to take a pic of the serious invasion.