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.
Send these straight over with Send to fertiliser comparison in the RO Mixer, or enter the Mixed result figures (or your own test-kit readings) by hand 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.
One difference worth knowing: the RO Mixer grades your water as a standing level — what is dissolved in it right now. The bands on this page grade ppm added per week by dosing. They are deliberately different measures, so the same figure can land in a different band in each tool without either being wrong. Calcium and magnesium are shown here as a baseline but have no weekly band, so they are not graded.
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.