EI and PPS-Pro dose planner: grams and milliliters for your tank

Two methods, two kinds of published numbers

The Estimative Index (EI) and PPS-Pro are the two dry-salt dosing schemes most often recommended for planted tanks, and they are published in different units. EI’s author describes the method in teaspoons per tank size plus target concentration ranges ^{[1, 2]}. PPS-Pro’s author publishes a gram recipe for two stock bottles and a daily dose in milliliters per volume of tank water ^{[3, 4]}. The planner keeps those published numbers visible and labels everything it adds on top as arithmetic.

EI mode: from a ceiling to grams

EI doses a deliberate surplus several times a week and resets the tank with a large weekly water change. The arithmetic behind it is stated in the original article: with a 50 % weekly change, a nutrient can build up to at most twice what is added each week, even if plants take nothing up ^[1]. In general the ceiling is the weekly addition divided by the fraction of water changed, so a 75 % change caps it at 1.33 times the weekly dose.

The planner runs that relationship backwards. You set the highest concentration you are prepared to see just before a water change, assuming no uptake, and it returns the weekly addition and the grams per dose. The defaults are 20 mg/L NO3, 2 mg/L PO4, 20 mg/L K and 0.4 mg/L Fe. They lie inside both published sets of EI ranges: NO3 5–30 (original) or 10–30 (EI Light), PO4 1.0–3.0 or 1.0–2.0, K 10–30 and Fe 0.2–0.5 “or higher” ^{[1, 2]}. A 20 mg/L nitrate ceiling at a 50 % change means 10 mg/L of nitrate a week, the same figure the original article uses as its worked example ^[1].

Potassium comes from three salts, so the planner first adds up what KNO3 and KH2PO4 already deliver and sizes K2SO4 only for the gap. If the nitrate and phosphate doses alone exceed your potassium ceiling, it says so and leaves K2SO4 out. Iron is dosed through the trace product you choose, using the manufacturer’s guaranteed iron percentage ^{[6, 7]}; the other trace elements that arrive with it are listed beside it.

EI Light lists its doses as teaspoons for five tank-size brackets, applied three times a week, with a “GH booster” once a week after the water change ^[2]. When your volume falls inside a bracket, the planner prints that row exactly as published. It does not convert teaspoons to grams, because EI Light gives no weights per teaspoon and the original article gives only one ^[1]. EI Light also says the scheme is not meant to be “written in stone” and that low-light tanks can dose less, and less often ^[2].

PPS-Pro mode: the published recipe, scaled

PPS-Pro’s macro bottle holds 29 g K2SO4, 33 g KNO3, 3 g KH2PO4 and 20 g MgSO4 per 500 mL; the trace bottle holds 29 g of a dry trace-element mix per 500 mL ^[3]. The daily dose is 1 mL of the macro solution and 0.5 mL of the trace solution per 10 US gallons or 40 L, which the author states delivers 1 ppm NO3, 0.1 ppm PO4, 1.33 ppm K, 0.1 ppm Mg and 0.05 ppm Fe a day. The same page says to use half the dose for lower light and double for very high light ^[4].

The planner scales that dose to your volume and light level, then recomputes the daily ppm from the recipe with IUPAC atomic weights ^[8] rather than repeating the stated figures. The two agree, which also shows that the recipe’s “MgSO4” has to be Epsom salt (the heptahydrate): only then do 20 g per 500 mL give 0.1 ppm magnesium per milliliter in 40 L. Iron depends on the trace mix you buy; with a 7 % iron product the computed figure matches the stated 0.05 ppm.

PPS-Pro aims at a lean water column. Its author lists ranges of 5–10 ppm NO3, 0.1–1 ppm PO4, 5–20 ppm K and 2–5 ppm Mg ^[5]. If you enter a weekly water change, the planner shows where each nutrient would settle with no plant uptake, which is an upper bound, not a forecast.

Worked example: 75 L, EI, 50 % weekly change, three doses a week

• NO3 ceiling 20 mg/L → weekly addition 10 mg/L → 3.33 mg/L per dose → 0.41 g KNO3 per dose.
• PO4 ceiling 2 mg/L → weekly 1 mg/L → 0.33 mg/L per dose → 0.036 g KH2PO4 per dose.
• Those two salts already add about 2.24 mg/L of K per dose; the K ceiling of 20 mg/L needs 3.33 per dose, so K2SO4 supplies the remaining 1.09 mg/L (0.18 g).
• With Plantex NutriTrace CSM at 7 % iron, a 0.067 mg/L Fe dose takes 0.071 g.

At these weights a 0.01 g kitchen scale is the limiting factor; a stock solution makes small doses easier to measure. The stock-solution calculator turns the same plan into milliliters.

Limits

• No uptake model. Every ceiling assumes plants take up nothing. Real tanks sit lower, by an amount that depends on light, CO2 and plant mass.
• Tap water counts. Nitrate, phosphate or potassium already in your tap water add to every figure; EI’s author says tap water nutrients mean you need to dose less ^[1], and PPS lists tap water as a source of nitrogen, phosphorus, magnesium and calcium ^[5].
• The methods differ in intent. EI floods and resets; PPS-Pro doses close to estimated daily use. The planner does not rank them.