Fertilizer dosing for planted tanks, without the guesswork.
Pick your tank and method. Get exact grams per dose or a stock-solution bottle recipe, the ppm each dose adds, a weekly schedule and calendar reminders.
- EI, lean EI, PPS-Pro, low-tech
- KNO₃ · KH₂PO₄ · K₂SO₄ · MgSO₄ · CSM+B
- L, US gal and UK gal
- Water-change aware
Weekly dosing chart
ppm added per dose and per week
Bar = weekly ppm; outlined band = educational range for that method family. "Builds to" = level just before each water change once dosing settles (weekly ppm ÷ water change).
Weekly schedule
After a water change
Water changes remove nutrients in proportion to the water removed. If you change less (or more) than the method assumes, this is the top-up that puts back what the change removed, at the level your plan settles at.
Common questions
Do I need K₂SO₄?
Only if KNO₃ and KH₂PO₄ don't already give you enough potassium. KNO₃ adds 0.63 ppm of potassium for every 1 ppm of nitrate. With EI's nitrate target you already get about 14 ppm K per week from KNO₃; K₂SO₄ fills the gap to 20–40. Low-tech tanks and tanks with potassium-rich tap water can usually skip it. The calculator shows how much K was short before K₂SO₄ was added.
Where does MgSO₄ go?
Most people add Epsom salt to the macro bottle or dose it dry right after the water change, since it is replacing hardness the change removed. Skip it if your tap water GH is moderate or hard (above roughly 4 dGH, check your water report or a GH test). Never put it in the iron (micro) bottle.
Why separate macro and micro bottles?
Phosphate and iron react and can drop out of solution as iron phosphate. Keeping CSM+B in its own bottle and dosing it on different days avoids that. The schedule above already puts micros on non-macro days.
Can I put Excel / liquid carbon in the bottle?
No. Glutaraldehyde products are dosed on their own, straight from their own bottle, per their label. Mixing them with fertilizer solutions is not something the makers support.
Grams vs teaspoons?
Teaspoon conversions depend on crystal size and packing, so this calculator gives grams. A 0.01 g jewelry scale costs little and removes the biggest dosing error. Below about 50 mg per dose, use stock-solution mode instead.
The salts and what they supply
Percentages are computed from IUPAC atomic weights. CSM+B is a blend; its numbers are a typical published label analysis, so check yours.
| Salt | Molar mass | Supplies (by weight) | Used for |
|---|---|---|---|
| Potassium nitrate KNO₃ | 101.10 g/mol | NO3 61.33 %, K 38.67 %, N 13.85 % | Nitrate (N) and potassium |
| Monopotassium phosphate KH₂PO₄ | 136.08 g/mol | PO4 69.79 %, K 28.73 %, P 22.76 % | Phosphate (P) and a little potassium |
| Potassium sulfate K₂SO₄ | 174.25 g/mol | K 44.88 %, SO4 55.12 % | Extra potassium without N or P |
| Magnesium sulfate heptahydrate (Epsom salt) MgSO₄·7H₂O | 246.47 g/mol | Mg 9.86 %, SO4 38.97 % | Magnesium (part of GH) |
| CSM+B trace mix chelated trace blend | blend | Fe 6.53 %, Mn 1.87 %, Zn 0.37 %, Cu 0.09 %, Mo 0.05 %, B 1.18 %, Mg 1.40 % | Iron and trace elements |
Popular guides
What is EI dosing?
The idea, the numbers and why the 50 % weekly water change matters.
Make a stock solution
Turn a dry salt kit into 500 mL macro and micro bottles.
How much nitrate and phosphate?
Target ranges for high-tech and low-tech tanks.
Seachem & Tropica doses
Label doses scaled to your tank, with the ppm they add.