Both methods remove phosphate effectively. They suit different tank sizes and different operator personalities.

GFO (granular ferric oxide)

Passive, predictable, slow. Set in a fluidized reactor and forget for 4–8 weeks. Safe for any reef.

Lanthanum chloride

Active, fast, requires careful dosing. Drip into a 5-micron filter sock to capture LaPO4 precipitate. Crashes phosphate fast — do not overdose.

Reef-keepers’ notes

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