Why dry-salt dosing
Bottled liquid fertilizers are convenient. They're also expensive, mostly water, and limited to whatever profile the manufacturer baked in. For a 200-litre planted tank running heavy lighting and CO₂, a year of commercial liquids easily clears €200. A year of the same nutrients in dry salts costs about €15 and lasts three years.
What you need is rarely complicated:
- __KNO₃ - potassium nitrate - provides NO₃ (nitrogen) and some K (potassium)
- __KH₂PO₄ - monopotassium phosphate - provides PO₄ (phosphate) and a little K
- __K₂SO₄ - potassium sulphate - provides only K, used to top up potassium
- A trace-element mix – CSM+B, TNC Trace, or your local equivalent – for iron and micros
The three popular profiles
Estimative Index (EI)
Created by Tom Barr in the early 2000s. The premise: dose nutrients in deliberate excess, do a large weekly water change (50%) to reset, and never have to worry about nutrient limitation. Weekly targets, roughly:
| Nutrient | Target (mg/L) |
|---|---|
| NO₃ (nitrate) | 20 – 30 |
| PO₄ (phosphate) | 2 – 5 |
| K (potassium) | 20 – 40 |
PPS-Pro
Lean dosing. Smaller daily doses, smaller water changes (10–20% weekly), aimed at "just enough" - tracks the same nutrients but targets levels plants will mostly consume between water changes.
EI Low / "Modest EI"
Halfway between the two. EI doses cut by 50%, water changes ~30% weekly. The setting most established planted tanks settle at after a couple of years of fiddling.
When to dose and when not to
Three principles cover most cases:
- __Dose before lights-on - plants take up most nutrients in the first 4 hours of the photoperiod.
- __Skip the water-change day - anything dosed gets siphoned out a few hours later.
- __Separate macros from micros by ~12 hours if you dose iron-heavy traces; phosphate + iron can co-precipitate.
The Redfield ratio (without the chemistry exam)
__The original Redfield ratio comes from marine plankton and is way too specific for what we do. In planted tanks, the practical version is: keep N : P at roughly 10:1 by mass. Too much phosphate relative to nitrogen - i.e., N : P below 5:1 - correlates with green-spot algae on slow-growing leaves and the front glass.
