It is often overlooked in aquaponic systems simply because it is seldom truly deficient. However, many aquaponic practitioners are not getting the best possible yields out of their flowering and fruiting crops because phosphorus (while not necessarily deficient) is not present in high enough amounts during critical stages in production.
The cause of many algae blooms (see: eutrophication) is phosphorus from industrial agriculture that has washed from cropland into rivers, streams, and eventually the ocean. Along the way, algae—often inhibited by lack of phosphorus—bloom, consume oxygen and turn waters that were once vibrant and ecologically diverse into green, dead sludge.
Read more at Upstart University (Nate Storey)