Dissolved nutrients. Sounds like a good thing, right? After all, every organism needs nutrients in one form or another in order to grow and stay in good health. So why are marine aquarium hobbyists—particularly reefkeepers—seemingly so fixated on keeping the level of dissolved nutrients in their systems as low as possible?
To understand this fixation, you have to keep in mind that the waters surrounding coral reefs are naturally nutrient-poor environments. Unless a reef is subject to agricultural runoff, sewage discharge, etc., the levels of dissolved nutrients around it never approximate what can accumulate in the closed system of a marine aquarium.
Elevated dissolved-nutrient levels lead to problems with nuisance algae and declining water quality, which is stressful or even deadly to marine livestock. That’s why hobbyists must implement different measures to export dissolved nutrients from their systems.
Here’s a sampling of basic nutrient-export techniques:
The routine water change
Protein skimming
Macroalgae
Rinsing or replacing mechanical filter media
Live rock and DSBs