Iron is of no importance in fish only aquaria; however, iron over 0.5 mg/L may be toxic to some species and should be avoided. Under normal conditions, iron is virtually impossible to maintain at measurable concentrations in seawater. Natural seawater concentration for iron is about 0.01 mg/L. Iron is important in planted aquaria and should be maintained between 0.1 to 0.2 mg/L.

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