The electricity drives the electrolysis of water that caused the chemical reactions growing dissolved minerals out of sea water. It also prevents all rusting of the metal. And it provides energy for the organisms exposed to the electrical field, causing faster growth and greater resistance to environmental stress. Without the electrical current these advantages are no longer present. We don't have much of a problem with algae blooms. These are temporary when water nutrients are too high, but go away by themselves, at least on Biorock projects (but not in natural reefs with excess nutrients from sewage and fertilizer, where the reefs are killed by algae).