EI and PPS-Pro, sized to your tank

Estimative Index

The EI approach, as the Barr Report's EI light guide puts it, adds a slight excess of nutrients so nothing runs out, then a large water change at the end of the week stops anything building up (Barr Report forum¹). The guide's table, also reproduced by NilocG Aquatics (NilocG Aquatics²), lists level-teaspoon amounts by tank size, each dosed 3 times a week with a 50% weekly water change. For low light it says smaller amounts can be used and the frequency cut to 1–2 times a week.

The guide gives these target ranges: CO₂ 20–30 ppm, NO₃ 5–30 ppm, K 10–30 ppm, PO₄ 1.0–2.0 ppm, Fe 0.2–0.5 ppm or higher, GH 3–5 and KH 3–5 (Barr Report forum¹).

The table gives trace elements as a teaspoon amount with a milliliter figure beside it and doesn't say which product. We list it as written and don't turn it into ppm.

PPS-Pro

Green Leaf Aquariums' PPS-Pro instructions mix two 500 mL bottles: macros with 29.3 g K₂SO₄, 32.6 g KNO₃, 2.9 g KH₂PO₄ and 20.2 g MgSO₄, and micros with 28.6 g CSM+B (Green Leaf Aquariums³). The dose is 1 mL of macros and 0.5 mL of micros per 10 gallons (40 L) daily before the lights come on, halved for low light and doubled for high light, with a 50% water change once a week. GLA states that at medium light this limits the water column to 14 ppm NO₃, 1.4 ppm PO₄, 18 ppm K, 1.4 ppm Mg and 0.7 ppm Fe. The calculator lands close to that (it uses 37.85 L for 10 gallons, where GLA rounds to 40). GLA writes only “MgSO₄”; we read it as the heptahydrate (Epsom salt), because that reading reproduces GLA’s own 1.4 ppm Mg.

Why the ceiling

If a tank gets a dose D every week and you change a fraction f of the water, the level just before the change approaches D ÷ f, however long you keep going. Plants only pull it lower. That's the arithmetic behind both schedules' weekly change, and why the 50% figure matters: halve the water change and the ceiling doubles.

Teaspoons are not grams

In a UK Aquatic Plant Society thread, a member weighed 10 teaspoons of each salt and got about 6.2 g for KH₂PO₄, 6.5 g for K₂SO₄ and 5.0 g for MgSO₄·7H₂O, and another member replied that EI generally assumes about 6 g per teaspoon (UK Aquatic Plant Society forum⁴). Grain size and how level the spoon is change it. The ppm here are only as good as that figure, so weigh your own spoon if you can.