The Estimative Index (EI) is a straight forward method for providing nutrients for a planted tank. The idea behind EI is simply introducing a non limiting amount of nutrients within an aquarium, throughout the week. This non limiting concentration 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 related issues are due to plant deficiencies rather than excess nutrient levels(Ammonium/NH4 + is a potential exception). Other issues for algae are too much light and most often poor CO2 measurement and dosing.

Basically you add a slight excess of nutrients to prevent anything from running out, then do a good sized 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. Fish aquarists do this same approach with Discus and other fish they want to feed heavily to increase growth rates/breeding.

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. You may dose dry powdered fertilizers or chose to make a stock solution and dose daily or 2-3x a week. This is your choice, if you are really into it and you feed your fish daily, then dosing the liquids work pretty well. There is no rule that you must use teaspoons, but it is easier for many new folks until they get more comfortable this the approach. you may also do larger than 50% weekly if you so chose and this will prevent less build up of nutrients. 50% weekly will keep the maximum possible build up to 2x the amount dosed for the week. So if you dosed 10 ppm of NO3, the most it would ever climb to is 20ppm as long as you did 50% weekly and no uptake took place. If you did a 90 % water change weekly, then the most it would build up would be about 12ppm. More work and effort to do the 90 % vs 50, but you get much smaller ranges, if you chose 25$, now you are at about 40ppm, so the difference in the % water changes can be used to change the build up and accumulation.

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 to medium 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
+/- 1/4 tsp GH booster once a week(water change only)
+/- 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
+/- 1/2 tsp GH booster once a week(water change only)
+/- 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
+/- 3/4 tsp GH booster once a week(water change only)
+/- 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 tsp once a week (water change only)
+/- 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
+/- 1.25 tsp once a week(water change only)
+/- 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 25-35 ppm
NO3 range 10-30 ppm
K+ range 10-30 ppm
PO4 range 1.0-2.0 ppm
Fe 0.2-0.5ppm or higher
GH range 1-2 degrees "extra" 17-40 ppm or higher

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
Gh booster

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.
No dosing method will save you from poor lighting(too much typically) or poor CO2 use. Also, try and find a routine that you can get into a habit of dosing, whether it is a liquid solution dosed daily, or dry powders dosed 2-3x a week etc, main thing is to be consistent with the dosing and watch the CO2 carefully.

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 acid (9 Molar, 1ml) can be added to prevent the mold. Some decide to make liquid stock solutions and dose the weekly totals daily over 7 days etc instead for narrower control. Some folks have high fish loading and add less N and P, it's really flexible and you should use common sense and try and tweak things.
It's not something that is or was designed to be written in stone to blindly follow. I'd much rather the aquarists think and use their own skill set to approach what's best for them rather than blind loyalty(a rather scary thought!).

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. Please note, this is not intended to be "written in stone", plants are flexible in their needs and demands, so getting away with less, or more is fine. As you gain more experience with plants, you may want to modify the routine to daily(see the thread in this section) or reduce or increase some parts. Most issues revolve around CO2 and water flow(which is related to gas and nutrient exchange in aquatic systems) if the nutrients are non limiting. Also, if you limit PO4 or NO3, you will not require nearly as much CO2. For example a NO3 level of 20ppm will require 2-3x as much CO2 to maintain growth over time as 2 ppm of NO3 (Gerloff, 1966). Of couse some who do not measure nor research things critically might be tempted to assume that low NO3 is why they solved their algae issue, however, it does not explain why other planted tanks are fine with 20ppm NO3 such as this one here(2.5 ppm PO4 and 30ppm NO3)


Secondary limitation will reduce CO2 demand....thus leading hobbyists to assume nutrients are the causes for their woes. However the real issue was low CO2 all along.
When that is addressed(and for some... it may be hard to do), then their no growth or algal issue.

So be highly critical of CO2 when approaching plant and algae growth, it's a key player and can drive growth rates 10-20X faster when used correctly. Make certain there is good ample water flow, plants, slow flow rates down by 90 % in thick groups (Barko et al, 1986).

John N and Tom Barr