EI light: for those less techy folks

Greg Watson

Staff member
Jan 23, 2005
United States
The Estimative Index (EI) is a straightforward method for providing nutrients for a planted tank. The idea behind EI is simply introducing an excess amount of nutrients within an aquarium, throughout the week. This excess of nutrients floods the water column and feeds the plants. This is an estimative method; measuring specific nutrient uptake rates is not necessary and no test kits are involved. EI provides a surplus of nutrients that helps to prevents plant deficiencies, and allows plant growth unhendered. Most algae releated issues are due to plant deficiencies rather than excess nutrient levels(Ammonium/NH4 + is the exception).

Basically you add a slight excess of nutrients to prevent anything from running out, then do a large water change at the end of the week to prevent anything from building up. This allows you to maintain a range of nutrients without ever using a test kit.

The water change generally takes about the same amount of time once you haul out the hoses etc do the water change so the time and work difference between a 25 % and 50% water change is fairly small.

The process of which this is done is simple. Each day (or 2-3x a week, weekly for low light tanks) fertilizers are dosed, and the nutrients are absorbed by the plants. With this method being estimative, we can dose fertilizers according to general guidelines suited for our particular setup (see below for regime). At the end of the week, one performs a 50% water change to ‘reset’ the nutrient load in the entire system. And then the entire dosing regime is repeated. The hobbyists can do larger(which will afford more accuracy) or smaller water change routines, but 50% is just guide line.

The primary fertilizers are the macro nutrients - Nitrogen (N), Phosphorous (P), Potassium (K), and the micro nutrients – trace elements (Plantex CSM+B, Flourish, Tropica Master Grow-TMG). Iron (Fe) can also be supplemented if necessary.

The Estimative Index method works best for a high light and well planted aquarium. However it is not limited to higher light setups, smaller quantities of fertilizers can be dosed if low light is used. Also, the frequency may be reduced to 1-2x a week at low light(1.5-2w/gal).

General Dosing Guideline for High Light and well planted aquariums.

10- 20 Gallon Aquariums
+/- 1/8 tsp KNO3 (N) 3x a week
+/- 1/32 tsp KH2PO4 (P) 3x a week
+/- 1/32 tsp K2SO4 (K) 3x a week
+/- 1/32 tsp (2ml) Trace Elements 3x a week
50% weekly water change

20-40 Gallon Aquariums
+/- ¼ tsp KN03 3x a week
+/- 1/16 tsp KH2P04 3x a week
+/- 1/16 tsp K2S04 3x a week
+/- 1/16 tsp (5ml) Trace Elements 3x a week
50% weekly water change

40-60 Gallon Aquariums
+/- 1/2 tsp KN03 3x a week
+/- 1/8 tsp KH2P04 3x a week
+/- 1/8 tsp K2S04 3x a week
+/- 1/8 (10ml) Trace Elements 3x a week
50% weekly water change

60 – 80 Gallon Aquariums
+/- 3/4 tsp KN03 3x a week
+/- 3/16 tsp KH2P04 3x a week
+/- 1/4 tsp K2S04 3x a week
+/- ¼ tsp (15ml) Trace 3x a week
50% weekly water change

100 - 125 Gallon Aquarium
+/- 1 1/2 tsp KN03 3x a week
+/- ½ tsp KH2P04 3x a week
+/- ½ tsp K2S04 3x a week
+/- ½ tsp (30ml) Trace 3x a week
50% weekly water change

Example Dosing Regime for 29 Gallon:
See attached file.

EI target ranges
CO2 range 20-30 ppm
NO3 range 5-30 ppm
K+ range 10-30 ppm
PO4 range 1.0-2.0 ppm
Fe 0.2-0.5ppm or higher
GH range 3-5 degrees ~ 50ppm or higher
KH range 3-5

See dosing calculators for additional dosing guides for Fe, etc.

Where to buy fertilizers?
Aquarium Plants, Aquatic Plants, Planted Aquariums, and Aquarium Plant Fertilizer can provide you with the necessary chemicals for dry and liquid dosing of the above. For micro - trace elements, Plantex CSM+B, Seachem Flourish, and Tropica Master Grow (TMG) are equivalent to each other. Fish Supplies, Online Fish Supplies, Aquarium Products, Aquarium Accessories at Big Al's Online for the Seachem and TMG brands.

1 lb of each for Greg Watson Chemicals will last at least 1 year:

Plantex CSM+B
Potassium Nitrate KN03
Monopotassium Phosphate KH2PO4
Potassium Sulphate K2S04

Special Notes:

Providing optimal CO2 levels of at least 30 ppm are necessary for plants to prosper. If algae issue arise, remove all visible algae and infected leaves. Recheck CO2 levels, and possibly reduce and adjust the lighting period.

Direct dry dosing into the tank is perfectly fine. Many dose straight into, or they dissolve each daily amounts in water before adding. Plantex CSM+B is often mixed into solution for liquid dosing. 1 tablespoon to 250ml water is equivalent to: 20 ml = 1/4 teaspoon of dry Plantex. This solution is stored in refrigerators to prevent mold from forming within the container. HCL can be added to prevent the mold.

Small dosing teaspoons (smidgen, dash, pinch) can be found at Linen & Things, Bed Bath and Beyond, Wal-Mart, dollar stores, eBay and other online retailers. To identify the specific measurements of your smidgen, dash, pinch set, a 1/8 tsp should fill a ¼ tsp in 2 tries, 1/16 tsp in 4 tries, and a 1/32 tsp in 8 tries.

Sticking to a good dosing regime will make your plants flourish, and keep you delighted! If you seek more in depth discussion about EI, there are two other articles here.

John N and Tom Barr