What all-in-one aquarium fertilizers declare on their labels

The labels

Three widely sold liquid fertilizers publish their composition on the manufacturer’s own product pages. Seachem lists Flourish per gram, with phosphorus as P2O5 and potassium as K2O ^[1]; Tropica lists its two products as weight-for-weight element percentages ^{[2, 3]}. Values not listed are “not published by the manufacturer”.

Element	Seachem Flourish	Tropica Premium	Tropica Specialised
N	0.07 % (total N)	0.0 %	1.3 %
P	0.0044 % (from 0.01 % P2O5)	0.0 %	0.1 %
K	0.31 % (from 0.37 % K2O)	0.8 %	1.0 %
Mg	0.11 %	0.4 %	0.4 %
Ca	0.14 %	not published	not published
S	0.2773 %	0.9 %	0.9 %
Fe	0.32 %	0.07 %	0.07 %
Mn	0.0118 %	0.04 %	0.04 %
B	0.009 %	0.004 %	0.004 %
Cu	0.0001 %	0.006 %	0.006 %
Mo	0.0009 %	0.002 %	0.002 %
Zn	0.0007 %	0.002 %	0.002 %
Other declared	Cl 1.15 %, Na 0.13 %, Co 0.0004 %	not published	not published

Flourish’s P and K are converted from the oxide forms on its label with the standard factors (P = P2O5 × 0.4364, K = K2O × 0.8302), because labels state phosphorus and potassium as oxides by convention ^[5]. See reading fertilizer labels.

Two things stand out. Flourish is an iron-and-trace product with almost no N or P, while Tropica sells the same trace base with and without N and P. And Seachem’s safety note on the Flourish page says the product contains 1,5-pentanedial (glutaraldehyde) and may produce an allergic reaction ^[1]; the liquid carbon guide covers that compound.

What one dose adds

To turn a label into mg/L you need the dose in grams. The labels give percentages by weight but no density, so the figures below assume about 1 g per mL, an approximation for dilute solutions. Recommended doses: Flourish 5 mL per 250 L once or twice a week ^[1]; Tropica 6 mL per 50 L once a week ^{[2, 3]}.

mg/L per recommended dose	Flourish (5 mL / 250 L)	Premium (6 mL / 50 L)	Specialised (6 mL / 50 L)
N	0.014	0	1.56
P (as PO4)	0.0027	0	0.37
K	0.061	0.96	1.2
Mg	0.022	0.48	0.48
Fe	0.064	0.084	0.084
Mn	0.0024	0.048	0.048

The arithmetic is the same for every row: milliliters × (percent ÷ 100) × 1000 ÷ liters, with mL taken as grams. Specialised’s 1.56 mg/L of nitrogen would be up to 6.9 mg/L if expressed as nitrate, but Tropica says the product contains both ammonium and nitrate ^[4], so the nitrate figure on a test kit would be lower.

How this compares with dry-salt methods

A single dose of any of these adds under 0.1 mg/L of iron (about 0.06–0.08 mg/L). EI aims for 0.2–0.5 mg/L iron in the water column ^[6], and EI Light treats Flourish as one of several interchangeable trace sources ^[6], dosed at its own rate rather than the bottle’s. A bottled all-in-one product fixes the proportions between nutrients; dry salts let you set each one separately. Neither approach is wrong, but numbers from one cannot be swapped into the other without converting.

What the labels do not tell you

• The form of nitrogen in Flourish, beyond “total nitrogen” ^[1].
• The chelating agent for iron and trace metals. Flourish’s iron is listed as derived from ferrous gluconate ^[1]; Tropica does not state the iron source on these pages.
• Density, which is needed for exact mg/L figures.

Products not covered

APT (2Hr Aquarist) and ADA publish fertilizer lines that are popular with aquascapers. Their composition could not be read on the manufacturers’ own pages when this page was checked on 12 October 2026, so they are not included. Reseller listings are not used as a substitute.