Can’t these be mitigated by UV and activated carbon though?
Edit - I can imagine large amounts of green algae and the soup of bacteria food they release could make activated carbon useless in a very short period, however.
Both UV and Activated carbon will moderate DOC but not completely. From what I've been abel to gather GAC can remove ~70% - 90% but still leaves some. How this remainder skews the microbial stuff is a question. UV will break down DOC but how the conversion of refractory DOC into compounds more readily utilized by microbes is a concern, espacially as one of the issues corals have is uncontrolled proliferation of microbes in their holobiont.