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.
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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.
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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