Dinoflagellates, in addition to being difficult to get rid of, can be a very harmful to your saltwater aquarium. Dinos, as they are often abbreviated, are photosynthetic protists that can very quickly bloom and take over your aquarium. The breakout can cover rocks, corals, and equipment in a thick brownish layer and any snail that eats it will most likely die due to the toxins given off by the dinos. To successfully get rid of dinoflagellates, you’ll need to take a multi-pronged approach. Turning off the lights for several days is a good starting point. This will deprive the dinos of much needed light energy used for photosynthesis. You will also need to perform several large water changes, run the protein skimmer 24/7, and add carbon and GFO into your media reactors. You may not have success immediately, but continually performing these steps will certainly get you closer to ridding yourself of dinoflagellates.