In Part I of this mini-series we spoke about all-in-one fertilizers, hitting on all of the good and the bad. Now we need to speak about another aquarium plant fertilizer system that is popular among advanced and aspiring planted tank and aquascaping enthusiasts: ESTIMATIVE INDEX (EI)

This system came about after years of work performed by Tom Barr, Ph.D where after a series of comparative experiments a baseline of macro and micronutrients was established for planted aquaria running medium-high to high light setups. All the various nutrients are purchased as dry powders and a graduated vessel is used to mix them in different ratios into water based on Dr. Barr’s Estimative Index. The resultant solutions are then dosed directly into planted aquariums.

With the EI method, there is a huge obvious benefit: Cost Savings. Purchasing dry powders which will then be (carefully!) measured out and then ultimately added into your aquarium for your plants’ nutritional needs is a much cheaper option than purchasing costly name-brand all-in-one fertilizers.

Another major benefit of the EI system is the ability to dial in individual nutrient dosing to meet any deficit your plants may encounter. Nitrogen, Phosphorus and Potassium are available as separate powders, and these are mixed into water in very specific amounts before use. This means that aquarists can get very detailed and specific regarding how much of these nutrients are added.

Normally the necessary micronutrient powder (CSM+B) is available pre-blended and is ready to use, and contains various ratios of magnesium, copper, iron, manganese, molybdenum, zinc, boron and EDTA. The amount of CSM+B is usually not adjusted up or down as are the macronutrients (Nitrogen, Phosphorus, Potassium) depending on results.

Not everything in the EI system is roses and smooth sailing though, in fact there are several major disadvantages. The first that we need to address is that it becomes too complicated to mix various powders in precisely the correct amounts daily for every aquarium that is kept. Usually, macro and micronutrients are not dosed on the same day and are staggered which adds even more to the complexity and offers more than ample opportunity for confusion, mis-measurements, missed or double doses and the resultant algae disasters.

Another issue that has become more manifest is the prevalence of low-quality powders that are available these days. As the popularity of EI increased, sources selling dodgy EI powders also increased and now there is no shortage of poor quality EI powders available across a number of e-commerce platforms.

While the EI dosing method offers extreme control and granularity over the nutrients added to your planted aquarium or aquascape, it is complex and easy to make mistakes with, and so this aquarium plant fertilizer system may not be the best fit for most aquarists. In our next (and final in this series) article, we will discuss our favorite dosing system: Neo-EI