Fertiliser comparison calculator
Pick any branded aquarium fertilisers and see exactly what each one delivers — nitrogen, phosphorus, potassium and the micronutrients — in ppm, at the manufacturer’s recommended dose or a dose you set. Normalise different brands onto the same scale and compare fairly.
Enter the Mixed result figures from the RO Mixer (or your own test-kit readings) in ppm. These are added to each product’s weekly dose so the columns show the total in-tank level. Leave a field at 0 to ignore it.
Source water is a standing level that is always in the tank, so the table shows per week while it is included — adding a permanent baseline onto a single dose would be misleading.
Understanding the numbers — dosing philosophies & how it works
Dosing philosophies — rough weekly targets
The badges in the analysis section place each product against three common approaches. These are approximate community guidelines, not rules — the right level depends on your light, CO2, plant mass and livestock. Figures are ppm added per week (as the compound your test kit reads).
| Nutrient | Lean | Standard | EI (high-tech) |
|---|---|---|---|
| Nitrate (NO₃) | < 5 | 5–15 | 15–30 |
| Phosphate (PO₄) | < 0.5 | 0.5–1.5 | 1.5–4 |
| Potassium (K) | < 10 | 10–20 | 20–35 |
| Iron (Fe) | < 0.1 | 0.1–0.25 | 0.25–0.5 |
Lean (e.g. 2Hr Aquarist / ADA style): keep nutrients modest so growth is controlled. EI (Estimative Index): dose to a comfortable surplus and reset with large weekly water changes. Standard sits between.
Why the iron ceiling is 0.5 ppm/week. Iron is the least agreed-upon of these bands, so it is worth being explicit. We use 0.5 ppm/week as the EI (upper) target because that is roughly what a standard Estimative Index trace dose (CSM+B) delivers, and about the point past which extra iron brings little benefit — it oxidises and precipitates quickly, can bind with phosphate, and higher levels are often linked (anecdotally) with algae. Lean and ADA-style dosing typically run iron far lower, around 0.1–0.2 ppm/week. Iron availability also depends heavily on the chelator (EDTA vs DTPA vs EDDHA) and light, so treat this as the softest of the four bands. Going higher (say a 1.0 ceiling) would make iron-lean all-in-ones look “unbalanced” simply because they hold iron back on purpose — which is why 0.5 is the more defensible middle-ground figure.
How it works
Every liquid fertiliser is roughly the density of water, so a declared 1% of a nutrient is about 10 mg per mL. The amount that reaches your water is then just:
ppm added = (nutrient % × 10) × mL dosed ÷ tank litres
Figures come from each manufacturer’s own guaranteed analysis or content declaration. Where a maker uses oxide notation (P2O5, K2O) we convert to the element; nitrogen can be shown as nitrate (NO3) and phosphorus as phosphate (PO4), which is what most test kits read.
A note on accuracy. Some brands (for example ADA, Easy Life, Aquario) treat their recipes as proprietary and don’t publish concentrations. Those are listed but marked “specs not published” — we never invent numbers. Always check the current bottle label before dosing, as formulations change. This tool is a planning aid, not dosing advice.
Working out CO2, water changes or remineralisation too? See the My Tank dashboard for pH/CO2 tracking and the RO mixer, or browse all AquaCalc tools.