Nutrient is an important component for plant growth and it can be categorized into 2 groups, Macro and Micro. Plants require in large amount of macro nutrients such as Nitrogen (N), Phosphor (P) and Potassium (K). In addition, plants require micro nutrients in small amount. Some aquarists classify micro nutrients as trace element (B, Ca, Co, Cu, Fe, Mg, Mn, Mo, Zn, Rb, Ni, V). 

Some aquascapers would micro manage fertilizer dosing but majority do not because most prefer to focus on creating beautiful scape instead. In order to overcome this, aquarist adopts the Estimate Index (EI). The idea is not new, method of growing plants using nutrient solution without soil has been commonly used in many hydroponic farms. In 2006, Tom Barr introduced the term; Estimate Index (EI) to the aquarium world and till today, the Estimate Index (EI) is widely accepted by many aquarists around the world.

From Tom Barr’s experiment, excess nutrients apart from Ammonia do not promote the growth of Algae. As such, aquarists can dose fertilizer without worry the fear of algae bloom. The idea behind EI is simply introducing an excess amount of nutrients within an aquarium. EI provides a surplus of nutrients that helps to prevent plant deficiencies, and allows plant growth unhindered. Coincidentally, healthy plants grow somehow hinder or slow down algae growth. At the end of the week, 50% water change is necessary to reset the fertilizer concentration so that there will be no toxic build up.

Based on the Tom Barr’s experiment:
1) The daily nutrients intake is roughly
         NO3 = 1-4 ppm
         NH4 = 0.1-0.6 ppm (Note: Dosing Ammonia will cause algae)
         PO4 = 0.2-0.6 ppm
2) The recommendation EI nutrients target per week
         NO3 = 5-30 ppm
         K+ = 10-30 ppm
         PO4 = 1-3 ppm
         Fe = 0.2-0.5 ppm

The above is based on the following assumptions:

1) The aquarium is densely planted with high light of at least 3 watts per gallon (WPG)
2) CO2 concentration of about 20-30 ppm

Therefore based on Tom Barr Estimate Index (EI) studies, the dosing guideline is as follows:

A. 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

B. 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

C. 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

D. 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

E. 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

In order to save cost, it is not recommended to use commercial fertilizers for this application. The most recommended type of fertilizer for EI are those dry form fertilizer such as KNO3, KH2PO4 and K2SO4. However, it does not mean that you cannot use commercial fertilizer for EI application.

In order to save some cost, we can measure the fertilizer intake of our stable aquarium weekly because common test kits are not sensitive enough to measure daily intake. A couple of test kits are required to measure the level of NO3, K and PO4 in your tank. You can start taking measurement after first month of tank setup. This is because after a month plants should be fully adapted to new environment and start growing.

During the dosage of dry fertilizer, make sure there is no chunk of dry fertilizer reaches your plants. Based on my encounter, I accidentally dropped a chunk of fertilizer inside a densely planted patch of Hemianthus Callitrichoides (HC). In a week’s time, I observed that the HC on that area starts to turn brown. Other plants species reaction may vary.

To prevent this from occurring, it is better to prepare your own liquid fertilizer by mixing dry fertilizer with water.

The following are based on my recommendation:
         1) Prepare 2 empty 1-liter bottles 
         2) For bottle 1 [KNO3]: Mix 1-liter of water with 253 grams of KNO3 (about 15 table spoons)
         3) For bottle 2 [KH2PO4 + K2SO4]: Mix 1-liter of water with 58 grams of KH2PO4 (about 4 tablespoons) and 18 grams of K2SO4 (about 1 tablespoon).

After preparing your liquid fertilizer, the next challenge is to determine how much to dose. Many online calculators are available online but my recommendations are as follows:

A. 13 Gallons (1.5 ft) tank
1ml of solution in bottle 1 add 3.15 ppm of NO3 and 1.99 ppm of K
1ml of solution in bottle 2 add 0.82 ppm of PO4 and 0.50 ppm of K

B. 18 Gallons (2 ft) tank
1ml of solution in bottle 1 add 2.27 ppm of NO3 and 1.43 ppm of K
1ml of solution in bottle 2 add 0.59 ppm of PO4 and 0.36 ppm of K

C. 50 Gallons (3 ft) tank
1ml of solution in bottle 1 add 0.82 ppm of NO3 and 0.52 ppm of K
1ml of solution in bottle 2 add 0.21 ppm of PO4 and 0.14 ppm of K

As for trace elements and Fe, just follow the instruction on the bottle.

With the above information, it is easy to calculate and determine how much liquid fertilizer is needed for each tank. It is so easy to make cheap and effective fertilizers for your aquarium. With this, I hope you can have great savings, controllable algae growth and most important more time to create great scape.