Seachem Flourish Potassium Review
A single-element potassium supplement for keepers who dose by components. It does one job — raise potassium without touching nitrogen or phosphorus — which makes it the fix for pinholes in leaves, not a standalone feed.
By the AquaVerdict Editorial Team · How we research & review
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Pros
- Targets potassium alone — adjust it without touching nitrogen or phosphorus
- The direct fix for classic potassium deficiency: pinholes and yellowing in older leaves
- Derived from potassium sulfate, so no unwanted nitrate or phosphate added
- Gentle and hard to overdose; a 500 mL bottle lasts a long time
Cons
- A single-element supplement — it is not a complete fertiliser on its own
- Only useful once you have diagnosed a genuine potassium shortfall
- Component dosing means more bottles and more thinking than an all-in-one
One nutrient, dosed precisely
Seachem Flourish Potassium does exactly one thing, and does it cleanly: it raises potassium in the water column without adding nitrogen or phosphorus. It is derived from potassium sulfate, so there is no stray nitrate or phosphate riding along — you adjust potassium and only potassium. That precision is the whole appeal. Potassium is one of the nutrients that runs down fastest in a fast-growing tank, and it is naturally low in soft or RO-based water, so being able to top it up in isolation is genuinely useful.
The tell-tale sign you need it is classic potassium deficiency: small pinholes and yellowing that appear first on the older, lower leaves. When the rest of your dosing looks right and that symptom shows up, this is the direct fix.
A component, not a complete feed
Be clear about what it is not. This is a single-element supplement, so it will never keep a planted tank fed on its own — plants also need nitrogen, phosphorus and the full trace set. It belongs in one of two places: a component dosing routine where you mix your own nutrients from separate bottles, or as a targeted add-on when a tank running an all-in-one and root tabs still shows a potassium shortfall specifically. Using it means more bottles and more thinking than a single all-in-one, which is the trade component dosers accept in exchange for surgical control.
How it fits with our other fertiliser picks
If you would rather not juggle single elements, a complete all-in-one like NilocG Thrive or Aquarium Co-Op Easy Green covers macros and micros in one bottle. For the trace/iron half of a component routine, see Seachem Flourish, and for heavy root-feeders add root tabs. Compare the whole range on the plant fertilizers hub, and match your dosing to the right substrate and lighting.
The scalpel, not the meal: a clean single-element potassium supplement for correcting pinholes and yellowing without touching your other nutrients. Invaluable if you dose by components, pointless as a tank's only fertiliser.
Where this one sits in its aisle
At 12 $, it is the 3 cheapest of the 10 models in this category published here.
- Cheapest in the aisle8 $
- Median13 $
- Dearest in the aisle37 $
Seachem Flourish Potassium — frequently asked questions
When do I need Flourish Potassium?
When plants show classic potassium deficiency — small pinholes and yellowing that start on older, lower leaves — and your other nutrients look fine. Potassium gets used up quickly in fast-growing tanks and is low in soft or RO-based source water. This supplement lets you raise it specifically without adding nitrogen or phosphorus, which an all-in-one would.
Can I use it as my only fertiliser?
No. It is a single-element supplement — potassium and nothing else. Plants also need nitrogen, phosphorus and a full set of trace elements, so on its own it will not keep a planted tank fed. It is a component you add to a routine, either to a DIY dosing regime or on top of an all-in-one and root tabs when potassium specifically runs short.
How does it differ from an all-in-one or from Leaf Zone?
An all-in-one bundles everything; Leaf Zone gives you potassium plus iron. Flourish Potassium is more surgical still — just potassium, derived from potassium sulfate so it adds no nitrate or phosphate. That precision is the point: it is for correcting one nutrient without disturbing the others, which is exactly what component dosers and deficiency-chasers want.
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Our score
7.8/ 10
The scalpel, not the meal: a clean single-element potassium supplement for correcting pinholes and yellowing without touching your other nutrients. Invaluable if you dose by components, pointless as a tank's only fertiliser.
Who this one is for
A planted keeper who dopes individual nutrients and needs to correct a potassium shortfall without altering nitrogen or phosphorus.
Compared with its closest rivals
Same category, nearest prices. Only the specifications every one of them states are shown — a half-empty column compares nothing.
| Model | Price | Type | Dosing | Contains | Best for |
|---|---|---|---|---|---|
| Seachem Flourish Potassium | 12 $ | Single-element supplement (potassium) | 5 mL per 30 US gal raises K by ≈ 2 mg/L | Potassium (from potassium sulfate) only | Correcting potassium deficiency; component dosers |
| Seachem Flourish Iron | 13 $ | Single-nutrient iron supplement | 5 mL per 200 L, 1–2× per week as needed | Iron (ferrous gluconate); no macros | Red and iron-hungry plants under good light |
| Seachem Flourish Tabs | 13 $ | Substrate root tablets (40 caps) | 1 tab per 10–15 cm of substrate, every 3–4 months | Micro-focused (Fe + traces), slow-release at roots | Heavy root-feeders in inert gravel or sand |
| Seachem Flourish | 13 $ | Comprehensive trace/micro supplement | 5 mL per 250 L, 1–2× per week | Micro-focused (Fe + traces); minimal macros | Low-tech tanks; micro top-up alongside macros |
What separates these models
- If price decides: this model, at 12 $.
- Highest Dosing in the table: Seachem Flourish (5 mL per 250 L, 1–2× per week).
If this one is not the right fit
- On a tighter budget: API Leaf Zone, at 8 $ in the same category. see the review
Price and availability
Details checked on July 16, 2026.
Sources
Specifications: manufacturer sheet and Amazon product page. Prices and availability: Keepa. No product on this site has been physically tested.
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