Iron is an essential element for plants, both aquatic and terrestrial: it is utilized in the production of chlorophyll and activates some enzymes that take part in metabolic reactions; it does all of this, however, in very small concentrations. Iron is considered a micronutrient, and it is often the limiting element in plant production in some aquatic habitats. This may be demonstrated by observing the increase in plant growth rates that occurs when iron is supplemented in systems in which it was previously immeasurable. Although this increase in plant growth may be desirable, it can be taken too far if iron supplementation exceeds the required concentration; in such an event, it is not uncommon to see increased growth of algae. This is particularly likely to occur in aquaria with excessive concentrations of nitrate and phosphate. As mentioned, iron is also required for the production of chlorophyll, which in turn is required for photosynthesis to occur. A deficiency of iron is physically apparent to the hobbyist as plant leaves which appear yellow or even somewhat transparent. In later stages, the leaves eventually disintegrate under gentle water current or disturbance. While this condition may also be caused by other chemical and environmental factors, it is seemingly most often the result of insufficient available iron (note that K, Mg, and N are also important).

Brightwell Aquatics Florin-Fe delivers iron in two steps: immediate and delayed. This is accomplished through natural biological and photochemical reactions taking place within all aquaria, and results in a more stable iron concentration than is attained with other methods of liquid iron supplementation. It is recommended that iron supplementation be performed on a daily, rather than weekly, basis. Doing so helps maintain a stable iron concentration (in opposition to adding it in large doses) that will enable the element to be taken up gradually by aquarium plants. Additionally, dosing in this fashion will minimize the chance of unwanted algae proliferation that is possible when a “megadose” of iron is delivered to the system all at once, creating a situation in which the iron is, at least temporarily, in a state of gross overabundance. Daily dosing also enables the hobbyist to witness the resultant changes taking place in the aquarium on a smaller time scale, further enabling them to increase or decrease iron dosage as conditions dictate; this is not easy, or perhaps even possible, when dosing once every 7 days, in which case changes may be drastic rather than subtle, and the perceived iron requirements of the aquarium become significantly more difficult to determine.