IME dino's appear when you bottom out your nutrients and then stay until they're outcompeted. Raising nutrient levels, instituting a fuge and continually blowing them off their perch have always killed them for me.
To elaborate, dinoflagellates are protists organisms -those that do not fit within the three natural kingdoms: animalia, plantae or fungus- with ability to move with rotating movements. All dinoflagellates have the common feature of having two flagella located at right angles allowing them to perform such rotational movement which makes them easily recognizable (although some species such as the genus symbiodinium they are virtually immobile).
There are about 2.400 species which have a highly variable size ranging from 20 and 300 µm in the most common ones and up to 2 mm in the case of species such as noctiluca. In the marine aquarium species are usual smaller as symbiodinium and Amphidinium, While some like ostreopsis are large and can be seen without a microscope (with good lighting and visual acuity).
The problem arises when conditions in the aquarium break the biological balance and some dinoflagellate species spread uncontrollably, smothering the rest of the aquarium inhabitants. If the dinoflagellate species in question has the ability to produce toxins (usual in ostreopsis, gambierdiscus and prorocentrum to name a few)
The problem often arises when we try to bring cleanliness it to the limit, in order to improve its appearance and color of corals.
They tend to occur suddenly when the aquarium water reaches an extraordinary cleanliness, in which most microorganisms perishes for lack of food. With no other organisms that can stop them, this type of dinoflagellate can multiply so fast that when we realize it's late and we will find an aquarium full of brown and ochre slime suffocating fish and invertebrates. These dinoflagellates possess chloroplasts enabling them to synthesize their own food even under a minimal amount of light. Some species can form cysts called pellicles which allow them to remain in the aquarium for months although we have completely sterilized or kept in complete darkness. Once the light or the right conditions come back, they will reappear and thus problems.
Most of these dinoflagellates have a very curious behavior, typical of pathogens and parasites. With the presence of light they secrete mucus which adhere to any surface, including algae, coral and fish. They spend hours synthesising food and extending vertically in search of the light source (if we turn off the pumps in the aquarium we can see brown filaments grow towards the surface). When the light source disappears and can no longer synthesize food, it begins to diminish to none.
