Question 1

What is the Estimative Index (EI) method?

Accepted Answer

The Estimative Index is a fertilization approach developed by Tom Barr that doses nutrients in excess of plant demand on a fixed weekly schedule, then resets with a 50% water change at the end of each week. By keeping all nutrients above deficiency thresholds at all times, EI eliminates the need to test for individual deficiencies.

Question 2

How often should I dose EI fertilizers?

Accepted Answer

Standard EI splits doses across the week: macros (KNO3, KH2PO4, K2SO4) on three alternating days, micros (CSM+B) on the three other days, and a 50% water change on day seven. A common schedule is macros Monday-Wednesday-Friday, micros Tuesday-Thursday-Saturday, water change Sunday.

Question 3

What if I don't have CO2 injection?

Accepted Answer

Low-tech tanks without CO2 use half-EI doses — the same schedule at 50% of standard amounts. Without CO2, plant growth is slower and nutrient uptake lower, so full EI doses would accumulate and promote algae. Half-EI maintains all nutrients above deficiency thresholds at a rate matched to low-tech growth.

Question 4

Do I need to dose all four EI components?

Accepted Answer

Yes. KNO3, KH2PO4 and K2SO4 supply nitrogen, phosphorus and potassium — the three macronutrients plants demand most. CSM+B supplies chelated trace elements including iron, manganese and zinc. Omitting macros causes visible deficiency symptoms; omitting traces causes pale new growth and iron deficiency.

Question 5

Can I use liquid fertilizers instead of dry salts for EI dosing?

Accepted Answer

Yes, but liquid all-in-one fertilizers are not designed for the EI protocol specifically and often contain lower concentrations than dry salts. For strict EI dosing, dry salts (KNO3, KH2PO4, K2SO4, CSM+B) are the standard. Liquid fertilizers work well for simpler low-tech setups or as a supplement to the EI schedule.

Fertilizer Dosing Calculator — EI Method

Standard EI Weekly Dosing Schedule

How the EI Method Works

Common Questions