It is a common misconception that Zoanthids and other soft corals like dirtier water, as opposed to the pristine water loving hard corals. In reality, all corals thrive best in water that is “clean” and they respond less favorably to water that is full of harmful organic matter that can inhibit growth and color. That said, soft corals tend to be more forgiving of certain water parameters, which makes them ideal for beginner reef keepers. Additionally, it is possible to have water that is “too clean” for certain corals. Corals require nutrients from various sources, which include photosynthesis and consuming various particles and live foods. If you take away one of these sources, for example by making the aquarium “clean”, then the corals just won’t do very well long term.