Seachem Flourish Iron Review
A targeted iron supplement for tanks whose plants — especially reds — want more iron than an all-in-one provides. A booster, not a standalone fertiliser.
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👍 Pros
- Highly available ferrous gluconate iron plants take up readily
- Deepens colour and greens up pale leaves on iron-hungry species
- Cheap, concentrated and lasts a very long time
- Lets you boost iron without over-dosing everything else in an all-in-one
👎 Cons
- A single-nutrient booster — it does nothing for macros or other micros
- Easy to chase 'redder' plants and over-dose; more iron is not always the fix
A booster, not a meal
Seachem Flourish Iron does one job: it adds readily-available iron, in ferrous gluconate form, that plants take up easily. That is genuinely useful for red and iron-hungry species that stay pale even when you are dosing a complete fertiliser — a targeted iron top-up can deepen colour and green up new leaves. What it will not do is feed a tank. It carries no nitrogen, phosphorus, potassium or other micros, so it only makes sense running alongside an all-in-one, which supplies the rest.
Dose with restraint
The main mistake here is chasing redder plants with ever more iron. Colour in red plants is driven mostly by light and CO2; iron is a supporting factor, not a magic switch. Start low — around 5 mL per 200 L once or twice a week — give the tank a couple of weeks to respond, and adjust only then. Over-dosing iron does not buy deeper reds and can nudge a tank toward algae. If the colour still will not come, look at your lighting and CO2 before adding more iron.
How it fits with our other picks
Flourish Iron is the add-on, so start with a complete base: an all-in-one such as Aquarium Co-Op Easy Green or the comprehensive Seachem Flourish supplement. Compare the full range on our plant fertilizers hub, and get the bigger levers right first with proper lighting and CO2.
A cheap, effective way to green up pale reds when a complete fertiliser is not quite enough on iron — provided you treat it as a targeted booster and resist the urge to over-dose.
Seachem Flourish Iron — frequently asked questions
Do my plants actually need extra iron?
Only some tanks do. A complete all-in-one already contains iron, and that is enough for most plants. Extra iron helps mainly with red and iron-hungry species that stay pale despite a full fertiliser routine — and even then, colour depends more on strong light and CO2 than on iron alone. Add Flourish Iron as a targeted boost when you see pale new growth on reds, not as a default.
How does an iron booster differ from an all-in-one?
An all-in-one liquid supplies macros (N, P, K) plus iron and traces — a complete diet dosed a few times a week. Flourish Iron is a single-nutrient top-up that only adds iron. You run it alongside a complete fertiliser, not instead of one; on its own it will not keep plants fed. Think of it as seasoning on top of a full meal.
Can I overdose iron?
Yes. It is tempting to keep adding iron chasing deeper reds, but too much does not help and can encourage algae or stress sensitive plants and livestock. Start at about 5 mL per 200 L once or twice a week, give the plants a couple of weeks to respond, and only then adjust. If colour still will not come, the limit is usually light or CO2, not iron.
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