Phytoplankton is a major part in ocean ecosystems, so it should be a major part in your aquarium as well. The number one goal for reef hobbyists should be to make the aquarium as similar to the ocean as possible. Adding phytoplankton is a fantastic way you can do exactly that.
There are several different phytoplankton products available to the reef aquarium hobby, but OceanMagik from AlgaeBarn is particularly useful because of the four species blend. More biodiversity is always better because it allows for balance and stability. What is great about OceanMagik is that each of the different phytoplankton species serve a separate purpose. They are like a team working together to make your aquarium flourish.
Nannochloropsis garditana or "Nano" for short helps remove ammonia, nitrites, and nitrates. This is extremally beneficial for those with a maxed out bio load. Tetraselmis sp or "Tet" serves as a food source for the aquarium. This phytoplankton species will feed your corals, making them appear fuller and more colorful. Isochrysis galbana or "Iso" for short helps to feed zooplankton and copepods. This is useful for those that are trying to maintain a copepods population, especially if you have a finicky fish. Along with that, Iso will improve coloration and resilience of the marine life in your aquarium. Lastly, Thalassiosira weissflogii or "Thal" competes with dinoflagellates by consuming silicates. Essentially, this algae will prevent or remove dinoflagellates from your aquarium.
Many hobbyist report that OceanMagik works amazingly for solving several different problems. Some say that they have tried several other phytoplankton products but claim none work as well as OceanMagik. This is because of the four species blend. All four species will help fight back algae by competing with it for phosphates and nutrients. This is not just some green liquid you are pouring in your aquarium because it might show results. It will show results. It is a tried and proved solution to several problems. Even if you aren't having any related problems, dosing phytoplankton will significantly help to prevent these issues from arising.
Another great thing about OceanMagik is the bottle. No, the bottle doesn't make the phytoplankton itself better, but it makes it easier to dose and measure. The double-neck bottle makes dosing the perfect amount easy and simple.