How much liquid fertilizer does my aquarium need?
Scale the exact bottle’s label to the water actually in the system. Include a running sump and subtract substrate, rock and the air gap. A tank’s advertised capacity can overstate the water receiving the dose. The true-volume calculator estimates that difference; a saved tank fills this page automatically.
Pick the product, then its schedule. Easy Green’s low-light starting routine is weekly, whereas the current APT 3 US directions are daily. Selecting a product resets the frequency and dispenser assumptions to that preset. Strength changes the amount in each application, not the number of applications. At 100 L, one Easy Green label dose is 2.64 mL; twice weekly uses 5.28 mL. Use your own bottle if its directions differ.
Read the variant carefully. Original Thrive is separate from Thrive+, C and S; Flourish comprehensive is separate from Flourish Excel. APT’s manufacturer says its regional and batch labels can differ. This preset uses the current US analysis, not an older APT Complete recipe.
Liquid fertilizer dose chart for 100 L of actual water
| Exact product | mL / dose | Label schedule | Dispenser reference* |
|---|---|---|---|
| Easy Green | 2.64 | 1× weekly low light; 2× medium; 3× high | 2.64 pumps / 52.83 drops |
| Thrive original | 5.28 | 1–2× weekly lower light; 3× higher light | Measure mL |
| APT 3 (US) | 3 | Daily | Measure mL |
| Flourish | 2 | Once or twice weekly | Measure mL |
| Tropica Specialized | 12 | Weekly; adjust to plant demand | 6 pumps |
| Tropica Premium | 12 | Weekly; adjust to plant demand | 6 pumps |
| Excel maintenance | 2.5 | Daily or every other day | 0.5 caps |
| Excel initial event | 12.5 | Initial / after >40% change only | 2.5 caps |
Full label doses, not the strength chosen above. Maker directions checked October 31, 2026. One product’s schedule does not apply to another.
*Optional Easy Green pump ≈1 mL; its dropper equivalent ≈20 drops/mL. Tropica pump = 2 mL; Seachem cap = 5 mL. Reference packaging only; custom dispenser settings above do not alter this chart. Measure fractions with a syringe.
Excel is an organic carbon supplement, not an NPK fertilizer. Initial dose is not a daily routine. Sensitive plants may react; consult the bottle and manufacturer guidance. Metric label volumes are used for Seachem because its gallon equivalents are rounded.
How do NPK percentages turn into nitrate and phosphate ppm?
In dilute aquarium water, 1 ppm is approximately 1 mg/L. For a mass-percent label, multiply the dose in mL by the density in g/mL, then by the percentage and 10 to get milligrams. Divide by the aquarium’s liters. Nitrogen reported as N needs a further factor of 4.427 for nitrate equivalent. P₂O₅ uses 1.338 for phosphate equivalent; K₂O uses 0.83 for elemental potassium.
Flourish and Tropica explicitly publish percentages by weight. APT and Thrive’s consulted pages do not specify the percentage basis, so treating those as mass percentages is an additional assumption. This tool starts at 1 g/mL as an estimate, not a measured product density. Weigh a measured volume after taring the container to obtain your bottle’s density. Easy Green instead uses its manufacturer’s rounded nutrient-per-dose table; its density field is unused.
Are Easy Green, Thrive, APT and Flourish interchangeable?
The same milliliters do not buy the same nutrients. Compare the weekly addition, since daily and weekly label doses differ. The table below applies each preset’s starting schedule; it is a label comparison rather than a ranking for plant growth. More light, plant mass, CO₂ availability and nutrients arriving in food change the demand.
| Product / starting frequency | NO₃ eq. | PO₄ eq. | K | Mg | Fe |
|---|---|---|---|---|---|
| Easy Green / 1× week | 3 | 0.162 | 2.01 | 0.18 | 0.034 |
| Thrive original / 1× week | 5.987 | 1.117 | 4.254 | 0.169 | 0.222 |
| APT 3 (US) / 7× week | 6.972 | 1.939 | 7.88 | 2.31 | 0.252 |
| Flourish / 1× week | 0.062 | 0.003 | 0.061 | 0.022 | 0.064 |
| Tropica Specialized / 1× week | 6.906 | 0.368 | 1.2 | 0.48 | 0.084 |
| Tropica Premium / 1× week | 0 | 0 | 0.96 | 0.48 | 0.084 |
ppm added per week at full label strength. All analysis-derived rows assume 1 g/mL and mass percentages; Easy Green uses published ppm. Nutrients already present and plant uptake are excluded. Amounts scale with water volume, so these ppm do not depend on tank size.
Do not use a trace supplement to chase a macro target. Flourish comprehensive contains only small N and P amounts; Tropica Premium has neither. The comparison therefore excludes these products when matching macros, but lets you compare iron. Even matching nitrate between two complete fertilizers leaves phosphate, potassium and trace ratios different.
Which fertilizer costs less for the same nutrient dose?
Enter the prices and sizes you actually buy, then choose a nutrient to match. In the 100 L, twice-weekly Easy Green example, the weekly addition is 6 ppm nitrate equivalent. Matching that with original Thrive takes about 5.29 mL per week at the assumed density. The table shows the other nutrient additions beside the matched amount, so a lower price cannot hide a different recipe.
A comparison that exceeds the other product’s published starting schedule is flagged. It is not permission to raise the dose; you would raise every nutrient in that bottle. For independently controlled macros, see the dry-salt dosing and stock-solution calculator. The EI guide explains the method and tradeoffs behind that approach.
How much Flourish Excel: initial dose or maintenance?
Looking for vodka, vinegar or NOPOX to manage marine nutrients? Use the separate reef carbon dosing calculator. Excel’s planted-tank label dose is not interchangeable with those routines.
Seachem’s directions distinguish a single initial dose from ongoing maintenance. For 100 L, the calculator gives 12.5 mL initially or after a water change exceeding 40%, versus 2.5 mL per maintenance application. Maintenance is daily or every other day. The larger initial amount must not become the daily setting.
Excel is an organic carbon supplement. Its manufacturer distinguishes it from dissolved CO₂ and straight glutaraldehyde. This page reports label milliliters, not an invented CO₂ concentration or glutaraldehyde ppm. It does not convert Excel into an equivalent injection rate.
Seachem reports that larger doses can affect Vallisneria, and recommends every-other-day use for sensitive Anacharis. Its marimo guidance advises starting smaller and watching for reactions. Do not spot-dose directly onto plants or use this tool to plan an overdose as algae treatment. A syringe is more reliable than a partial cap.
Why is nitrate still rising, or plant growth still poor?
A dose is an addition, not a prediction of the test result. Food, tap water, substrate and existing nutrients add to the starting point; plant uptake and water changes remove some. This calculator’s accumulation figure isolates fertilizer input with zero uptake and nutrient-free replacement water. It reuses the same mass balance as the dry-fertilizer tool.
The twice-weekly Easy Green example adds 6 ppm nitrate equivalent per week. With a 50% weekly change and no uptake, the eventual pre-change contribution reaches 12 ppm. With no changes and a positive net addition, the model has no finite ceiling. Real plants make this an illustrative upper bound for that fertilizer contribution, not a total-water reading.
If a test keeps climbing, verify the bottle variant, dispenser output and actual water volume first. Check source water and compare readings at the same point in the dosing cycle. Poor growth alone does not prove a fertilizer shortage; review lighting and carbon availability before adding more. Use the water-change calculator for an existing nitrate buildup and the CO₂ tool for the limits of estimating dissolved gas from pH and KH.
Manufacturer labels used in this calculator
Checked October 31, 2026. These presets describe the linked formulas; a changed or regional bottle label takes precedence. Pumps are packaging-specific, including Aquarium Co-Op’s optional replacement pump. The chart uses Seachem’s metric rates consistently because the printed gallon equivalents are rounded.
- Aquarium Co-Op Easy Green — Uses the manufacturer’s rounded nutrient-per-dose table, not a density inferred from its analysis.
- NilocG Thrive — original — Original Thrive only. Thrive+, Thrive C and Thrive S have different formulas. Percentages treated as mass fractions; density must be assumed or measured.
- 2Hr Aquarist APT 3 — US label — Current US web analysis. EU and older APT Complete labels differ: use this preset only if your bottle matches. Percentage-as-mass is an estimate.
- Seachem Flourish — comprehensive — Primarily a trace supplement. Do not increase it to chase a nitrate or phosphate target. Seachem confirms analysis is percentage by weight.
- Tropica Specialized Nutrition — Analysis is W/W and lists elemental P and K, not P₂O₅ and K₂O. Nitrate equivalent is not necessarily immediate nitrate.
- Tropica Premium Nutrition — Contains no nitrogen or phosphorus. W/W percentages; elemental P and K basis.
Seachem’s Excel dosing tables provide the separate initial and maintenance references. Always measure the liquid actually delivered; a pump stroke or drop is an estimate.