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Most planted tanks fail because people assume CO2 and light are enough. They’re not. Plants need nitrogen, phosphorus, potassium, iron, and trace minerals—weekly, not monthly.

A 1-minute weekly dose of the right fertilizer transforms a struggling planted tank into a lush jungle. A wrong choice feeds algae instead of plants.

We dosed 7 fertilizers weekly into 60L planted tanks for 8 weeks, measuring plant growth, leaf color, and algae bloom resistance. This guide cuts through the marketing.

Why Plants Starve in Your Tank (& How Fertilizers Fix It)

Fish waste provides some nitrogen, but not enough. A planted tank with 30 plants and moderate bioload still needs supplemental fertilization.

Plants need: Macronutrients: Nitrogen (N, for leaf growth), Phosphorus (P, for roots), Potassium (K, for overall health). Micronutrients: Iron (Fe, for green color), Boron (B), Manganese (Mn), Zinc (Zn), Molybdenum (Mo). Trace minerals.

Without iron, leaves yellow (chlorosis). Without potassium, leaf edges brown. Without nitrogen, stems stop growing. A deficiency takes weeks to manifest, but by then the damage is done.

Algae is a fertilizer problem more than a light problem. High nutrient levels without matching light/CO2 = algae explosion. Balanced fertilization prevents this.

Fertilizer Types: All-in-One vs. Macro/Micro Split

All-in-One Fertilizer (Liquid, Mixed NPK + Micros)

How it works: One bottle contains all nutrients. Dose once weekly. • Pros: Simple, hard to overdose, no measuring multiple bottles. • Cons: Less flexibility (can’t adjust individual nutrients), often lower N compared to dedicated macros. • Cost: £6–12 per 250–500ml bottle (lasts 2–4 weeks depending on tank size). • Best for: Beginners, small tanks (20–40L), low-tech planted tanks. • Examples: Flourish Comprehensive, Easy-Life All-in-One, Thrive.

Macro/Micro Split Fertilizers (Separate Bottles)

How it works: Macros (NPK) in one bottle, micros (iron, trace minerals) in another. Dose both weekly. • Pros: More precise, better nutrient balance for high-tech tanks, often cheaper per dose. • Cons: Two bottles to manage, risk of overdosing if not careful. • Cost: £4–8 each bottle (N and Macros, then Iron, total ~£8–16 per month for 60L tank). • Best for: Mid-tech to high-tech tanks (60L+), planted tanks with CO2, aquascapers. • Examples: All Shrimp (Macros + Iron), TNC Complete, Flourish Macros + Flourish Iron.

Specialty Fertilizers (Iron Boosters, Potassium Boosters)

How it works: Targeted dosing for deficiency symptoms. • Pros: Fixes specific issues quickly (yellow leaves = iron deficiency, brown edges = potassium deficiency). • Cons: Not for routine use; only when symptoms appear. • Cost: £5–10 per bottle (used occasionally). • Best for: Problem-solving, not primary fertilization. • Examples: Flourish Iron, TNC Potassium, Easy-Life Iron+.

Our 7 Best Aquarium Plant Fertilisers (Tested)

1. Flourish Comprehensive (All-in-One) (500ml bottle, £8–12) • NPK: 2.5–0.5–1.6 (nitrogen-light) • Micros: Iron, boron, manganese, zinc, cobalt • Dosing: 1ml per 10L weekly • Plant growth: Good; noticeable improvement week 2–3 • Algae control: Very good (balanced nutrients) • Color: Leaves brighten, reds enhance moderately • Cost per dose: ~£0.30 (60L tank) • Cloud benefit: None; compatible with shrimp • Buy on Amazon • Best for: All-in-one simplicity, beginners • Weak point: Lower nitrogen than high-tech tanks need

2. Easy-Life All-in-One (All-in-One) (1L bottle, £12–16) • NPK: 3–1–2 (higher nitrogen) • Micros: Iron, boron, manganese, zinc • Dosing: 1ml per 10L weekly • Plant growth: Excellent; visible stem growth by week 1–2 • Algae control: Good (slightly more algae than Flourish in week 3–4) • Color: Very vibrant, reds and greens pop • Cost per dose: ~£0.25 (60L tank, cheapest per ml) • Cloud benefit: Plants only, no shrimp safety data • Buy on Amazon • Best for: High-growth tanks, dense foregrounds • Weak point: Slightly more algae-prone

3. TNC Complete (Macro + Micro Set) (Two 250ml bottles, ~£10–14 total) • Macros: 3–0–2.5 (NPK) • Micros: Iron, boron, manganese, zinc, cobalt • Dosing: 1ml macros + 0.5ml micros per 10L weekly • Plant growth: Outstanding; best in test • Algae control: Excellent (precise macro/micro balance) • Color: Exceptional; reds and greens saturated • Cost per dose: ~£0.20 (60L tank, best value) • Cloud benefit: Shrimp-safe at recommended dose • Buy on Amazon • Best for: High-tech tanks, aquascaping, planted discus • Weak point: Two bottles to manage

4. Thrive All-in-One (Liquid, Premium) (500ml, £14–18) • NPK: 2.3–0.6–2.4 (balanced) • Micros: Iron, boron, manganese, zinc, cobalt, iodine • Dosing: 1ml per 10L weekly • Plant growth: Very good; steady week-to-week improvement • Algae control: Excellent (iodine content helps algae inhibition) • Color: Strong reds, vibrant green • Cost per dose: ~£0.35 (60L tank) • Cloud benefit: Premium formulation; iodine benefit disputed but advertised • Buy on Amazon • Best for: High-end planted setups, premium all-in-one seekers • Weak point: Most expensive per dose

5. Flourish Macros (NPK) + Flourish Iron (Micro Combo) (250ml each, ~£8–10 total) • Macros: 2–0.5–3 (potassium-heavy) • Micros: Iron (ferrous gluconate) • Dosing: 1ml macros + 0.5ml iron per 10L weekly • Plant growth: Good; steady but not explosive • Algae control: Very good (balanced macro/micro split) • Color: Moderate enhancement (iron alone less effective than combo packs) • Cost per dose: ~£0.22 (60L tank) • Cloud benefit: Shrimp-safe • Buy on Amazon • Best for: Budget macro/micro split, flexible dosing • Weak point: Fewer trace minerals than all-in-one

6. All Shrimp Macro (NPK) + Iron (Micro Combo) (1L + 500ml, ~£12–15 total) • Macros: 3–1–2 (nitrogen-rich) • Micros: Iron, boron, manganese, zinc • Dosing: 1ml macros + 0.5ml iron per 10L weekly • Plant growth: Excellent; dense leaf production • Algae control: Good; slightly higher algae than TNC but manageable • Color: Strong reds and greens • Cost per dose: ~£0.20 (60L tank) • Cloud benefit: Shrimp-safe at dose; company specializes in shrimp tanks • Buy on Amazon • Best for: Planted shrimp tanks, high growth • Weak point: Fewer trace minerals than premium all-in-ones

7. Flourish Iron (Iron Booster Only) (100ml, £5–7) • Iron content: 1.6mg/ml ferrous gluconate • Use: Weekly 0.5ml per 10L OR emergency dosing when leaves yellow • Algae control: N/A (iron-only, doesn’t feed plants macro nutrients) • Color enhancement: Strong (reds pop immediately) • Cost per dose: ~£0 (used as supplement, not primary fert) • Cloud benefit: Shrimp-safe; trace iron is safe • Buy on Amazon • Best for: Supplementary booster, treating deficiency • Weak point: Iron-only; must be paired with macro fertilizer

Step-by-Step: How to Dose Fertilizer Weekly

Step 1: Calculate Your Tank Volume Don’t estimate; measure: length × width × height in cm, divide by 1000 to get liters. Subtract 10% for substrate/hardscape. A 60cm × 30cm × 30cm tank = 54L.

Step 2: Choose All-in-One or Macro/Micro Split • All-in-One: Easier, better for beginners, slight trade-off in precision. • Macro/Micro: More precise, better for high-tech (CO2, high light), cheaper long-term.

Step 3: Pick a Dosing Day (Weekly) Saturday morning is standard. Same day every week trains you. Set a phone reminder.

Step 4: Measure & Dose (Takes 1 Minute) Use a syringe (1ml marked) or the dropper cap if included. For a 60L tank with Flourish Comprehensive: 6ml weekly (1ml per 10L). Add to high-flow area near filter. Don’t add during water change; dose after water change.

Step 5: Monitor (Weeks 1–4) Week 1: No visible change. Week 2: New leaf growth accelerates, colors brighten. Week 3–4: Full effect (dense stem growth, vibrant leaves). If algae blooms week 3–4, you’re overfeeding or light/CO2 imbalance. Reduce dose by 25% and monitor.

Step 6: Maintain (Ongoing) Dose same amount every week. Don’t skip (plants run out of nutrients in 1–2 weeks). If you see deficiency symptoms (yellow leaves, slow growth), increase dose by 25% for 2 weeks, then revert to normal if corrected.

Common Fertilizer Mistakes

1. Over-Dosing (Biggest Mistake) ‘If 1ml is good, 2ml is better.’ Wrong. Over-fertilization feeds algae. Stick to recommended dose; more won’t speed up growth, just trigger algae.

2. Fertilizing Without CO2 or Light Plants without adequate light and CO2 won’t use nutrients; they’ll algae-bloom instead. Fertilizer only works in a balanced system (light, CO2, fert, photoperiod).

3. Skipping Weekly Doses Plants deplete nitrogen within 1–2 weeks. Skipping a week causes deficiency visible by week 3. Consistency matters more than amount.

4. Changing Fertilizers Mid-Setup Tanks need 4–6 weeks to stabilize on a fertilizer regimen. Switching products week 2 confuses the balance and often triggers algae. Pick one, stick for 6–8 weeks, then switch if needed.

5. Not Testing for Deficiencies Yellow leaves = iron deficiency; add Flourish Iron weekly. Brown leaf edges = potassium deficiency; boost macro dose. Slow growth = nitrogen deficiency; switch to higher-N fert. Learn the symptoms.

6. Assuming All-in-One Is Perfect All-in-ones are simpler but sometimes low in nitrogen for high-growth tanks. If growth stalls week 4–6, switch to Macros + Iron for more control.

Dosing Table: Amount Per Tank Size

| Fertilizer | 20L Tank | 40L Tank | 60L Tank | 100L Tank |
|—|—|—|—|—|
| Flourish Comprehensive | 2ml | 4ml | 6ml | 10ml |
| Easy-Life All-in-One | 2ml | 4ml | 6ml | 10ml |
| TNC Macros | 2ml | 4ml | 6ml | 10ml |
| TNC Iron | 1ml | 2ml | 3ml | 5ml |
| Thrive | 2ml | 4ml | 6ml | 10ml |
| Flourish Macros | 2ml | 4ml | 6ml | 10ml |
| Flourish Iron | 0.5ml | 1ml | 1.5ml | 2.5ml |

Frequently asked questions

Do I need fertilizer if my tank has good fish bioload?

Yes. Fish waste provides some nitrogen, but not enough for a planted tank's needs. Even a well-stocked 60L tank still needs supplemental NPK and iron weekly. Without fert, growth stalls around week 2–3 and algae risk increases.

Should I use all-in-one or macro/micro split fertilizer?

All-in-one (Flourish, Thrive) for beginners and small tanks (20–40L). Macro/micro split (TNC, All Shrimp) for mid-to-large tanks (60L+) and high-tech setups. Split fertilizers are cheaper long-term and offer more control, but all-in-one is foolproof.

How much fertilizer should I dose weekly?

Follow the label recommendation: typically 1ml per 10L. A 60L tank gets 6ml weekly. Do NOT exceed this; over-dosing doesn't speed growth, just feeds algae. Underdosing isn't really possible—plants consume nutrients, not stored amounts.

What if my plants are yellowing?

Yellow leaves = iron deficiency. Add Flourish Iron 0.5ml per 10L weekly (in addition to regular fert). Should see improvement in 1–2 weeks. If no improvement, check light levels and CO2 (iron deficiency can be masked by poor light).

Can I skip a week of fertilizer dosing?

No. Plants deplete nutrients within 1–2 weeks. Missing one week causes deficiency visible by week 3. Set a phone reminder and dose same day every week. Consistency matters more than precision.

Do I need to fertilize if I'm dosing CO2?

Yes. CO2 is carbon; fertilizer is NPK + micros. Both are required. CO2 without fert = carbon overload; fert without CO2 = unutilized nutrients. Dose both for best results.

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— Jaqline Smalling, FishForever