Why EI Works
In a high-light, CO2-injected tank, plants grow at maximum rate and use nutrients fast. Running out of any single nutrient = stunted growth + algae.
EI solves this by deliberately providing more than plants can use. The 50% weekly water change resets the tank, preventing nutrients from accumulating to toxic levels.
Tom Barr developed and popularized EI in the early 2000s. It is now the dominant approach in the high-tech community.
Standard EI Doses
Per 50 gallons (3× per week, alternating with micros):
• 1/4 tsp KNO3 (potassium nitrate) — provides N and K.
• 1/16 tsp KH2PO4 (mono potassium phosphate) — provides P and K.
• 1/4 tsp K2SO4 (potassium sulfate) — provides extra K.
Per 50 gallons (3× per week, alternating with macros):
• 1/16 tsp CSM+B (Plantex Comprehensive Solution + Boron) — provides Fe and trace metals.
Schedule
Day 1 (Sunday): macros
Day 2 (Monday): micros
Day 3 (Tuesday): macros
Day 4 (Wednesday): off
Day 5 (Thursday): micros
Day 6 (Friday): macros
Day 7 (Saturday): 50% water change, no dosing.
Scaling to Your Tank
For 20-gallon: half the standard 50-gallon dose.
For 75-gallon: 1.5× standard dose.
For 125-gallon: 2.5× standard dose.
For 180-gallon: 3.5× standard dose.
Dry vs Liquid
Dry chemicals (KNO3, KH2PO4, K2SO4, CSM+B): cheapest. 1 lb of each lasts 1–2 years for a 75-gallon tank. Total cost ~$30.
Premixed liquid (Nilocg Thrive, GLA EI Salts dissolved): convenient, 5× the cost.
PPS-Pro Alternative
PPS-Pro (Perpetual Preservation System) is a leaner alternative — daily small doses, no water-change reset required.
Better for low-stocked, lightly fed tanks. EI is better for heavily stocked, heavily fed tanks.
Adjustments
Yellow new growth: increase iron (CSM+B) or add Flourish Iron mid-week.
Pinholes in leaves: increase potassium (K2SO4).
Stunted new growth + dark old leaves: increase nitrate (KNO3).
Brown/black algae: water flow + CO2 issue, not nutrient.