NilocG Thrive C vs Seachem Flourish: Complete or Supplement?
NilocG Thrive C vs Seachem Flourish: one is a complete all-in-one fertiliser, the other a micros-only supplement that starves plants alone.
They aren't the same kind of product. NilocG Thrive C is a complete all-in-one fertiliser — it has the macros (nitrogen, phosphorus, potassium) and micros plants need. Seachem Flourish is a trace/micronutrient supplement only, with no significant nitrogen or phosphorus, so it starves plants if run alone. For one bottle that does it all, buy Thrive C; use Flourish only to top up micros alongside a macro source.
| Product | Score | Nutrient Completeness | Dosing Control | Algae Risk | Owner Satisfaction | Value | Buy |
|---|---|---|---|---|---|---|---|
| NilocG Thrive C All-in-One (500 mL) NilocG · mid-range | 90 | 100 | 100 | 98 | 80 | 77 | Buy → |
| Seachem Flourish Comprehensive (500 mL) Seachem · budget | 92 | 96 | 100 | 98 | 82 | 87 | Buy → |
| API Leaf Zone (18 oz) API · budget | 90 | 84 | 100 | 98 | 82 | 87 | Buy → |
They are not the same product
This is the mix-up that stalls more planted tanks than any other. Both bottles say "for planted aquariums," but they do different jobs. A complete fertiliser has both macros (nitrogen, phosphorus, potassium) and micros (iron and trace elements). A supplement has only part of that. Buy the wrong one to use alone and your plants slowly starve for whatever it leaves out.
What each one is
- NilocG Thrive C — complete. An all-in-one with N, P, K and micros, tuned low for low-tech tanks. One weekly dose covers everything a water-column plant needs.
- Seachem Flourish — supplement. A rich trace/micro blend, but Seachem's own page states it "does not contain significant levels of nitrogen or phosphorus." It is designed to supplement micros, not to feed a tank on its own.
Run Flourish alone and plants starve
Dose only Flourish and your plants get iron and trace elements but no nitrogen or phosphorus to build tissue — so growth stalls and older leaves yellow and die back. That is not a knock on Flourish; it is doing exactly what it is designed for. It just is not a standalone fertiliser, and a lot of beginners buy it thinking it is.
When Flourish is the right call
Flourish shines as a top-up next to a macro source: if you dose dry salts or a macro-focused fert and just want to add trace elements, Flourish is excellent. It is also a fine iron/micro booster for a tank that is otherwise fed. (The same logic rules out API Leaf Zone as a standalone — it is essentially iron and potassium, no N or P — good as a cheap top-up, not a complete fert. See our full guide to fertilising a low-tech tank.)
Bottom line
Want one bottle that does it all? Buy NilocG Thrive C — it is complete. Reach for Seachem Flourish only to top up trace elements alongside a macro source, not as your only fertiliser. Read the label: if it does not list N, P and K, it is a supplement, not a standalone.
Thrive C is a complete fertiliser; Seachem Flourish is a micros-only supplement (Seachem's own page says it has no significant N or P). Run alone, Flourish starves plants — so for a single all-in-one bottle buy Thrive C, and use Flourish only to top up trace elements next to a macro source.
Common questions
Can you use Seachem Flourish as your only fertiliser?
Not for a growing planted tank. Seachem's own page states Flourish has no significant nitrogen or phosphorus, so used alone it starves plants of macronutrients. It is a micronutrient supplement, best paired with a macro source.
Is NilocG Thrive C a complete fertiliser?
Yes. Thrive C is an all-in-one that includes macronutrients (nitrogen, phosphorus and potassium) alongside micronutrients, so it can be the single bottle for a low-tech planted tank.
Which is better for a low-tech planted tank?
For most low-tech tanks a complete all-in-one like Thrive C is simpler and enough on its own. Flourish makes sense only as a micronutrient top-up alongside a fertiliser that already supplies the macros.