Estimative Index

The Estimative Index, usually shortened to EI, is a method for supplying nutrients to aquarium plants. Its aim is to keep nutrients available in the water so that a shortage does not limit plant growth.

You add a small surplus of nutrients during the week, followed by a water change of at least 50% at the end of the week. This limits the build-up of unused nutrients and gives you a repeatable starting point for the next week's dosing.

Nutrients are only part of the picture. Too much light for the available CO2, poor circulation and interruptions to plant growth can all contribute to algae problems. Adding more fertiliser alone will not solve every problem.

The method described here assumes a weekly water change of at least 50%, adequate CO2 and enough water movement to distribute nutrients. The original guide uses a CO2 target of at least 25 ppm; treat this as a dosing assumption rather than a reason to increase CO2 without checking your aquarium and watching its livestock.

Create a weekly schedule for your aquarium

Our calculator helps you make a dosing schedule and add the required products to your cart. If your plants or water tests show that a particular nutrient is too high or too low, adjust that part of the dose.

Create your dosing schedule in three steps

Read more in the AquaInfo introduction to EI (Dutch) or the UKAPS guide to dosing with dry salts.