Aquatopia
New Member
The Estimate Index (EI) system of aquarium fertilisation for aquarium plants is a complex and often misunderstood system. Because of this it is often found not to work for people and/or is given up on as a fertiliser.
I avoided using it because of the complexity and the amount of varying information that was available on the subject. I don't like to use anything that I don't understand and trying to understand the EI system was problematic so I left it alone in favour of using commercial fertilisers.
Only when it came to preparing for my current tank build did I decide that the time had come for me to get to grips with it. The large volume of water in my new tank meant that using commercial fertilisers was no longer financially viable. It would be way too expensive.
I set about learning the EI system and soon came across something called the 'IFC Aquarium Fertilizer Calculator'. This is an Excel based spreadsheet calculator written years ago by some very clever people from a UK based Aquatic Plant Forum.
I'd post a link but I don't want to advertise another forum here. If you Google 'IFC Aquarium Fertilizer Calculator' though you will certainly find it anyway.
It is this spreadsheet calculator that is critical in working out your own 'recipe' for the EI Fertiliser system. I will be posting screenshots of the values I have entered into the spreadsheet to show you how I got to the amounts I use for dosing, so if you want to follow along or try this for yourself then you will need to download the 'IFC Aquarium Fertilizer Calculator'. The current version (as I write this) is v1.3.1 and this is the version I have used.
When it comes to the EI fertiliser system there are multiple ways to create the mixture(s) that you dose to your tank as well as multiple different ways of actually dosing. This is what makes the EI system so confusing, I think anyway. It took me a while, and a lot of questions, to finally figure out what was going on.
I'm not going to go into the details of all the different ways that you can do the EI system, suffice for you to know that there are multiple ways and all of them work just as well. Different people use the different ways, either through preference or belief that a particular way is 'better' for them. No one way has had more success than any other though, they all work just fine. If you want to look more into any of the other ways, or would like even more technical details, then I would suggest reading all the information on the forum where the 'IFC Aquarium Fertilizer Calculator' comes from.
Because there are all the different ways to do EI Fertiliser they have become mixed up and misunderstood. For example, people read about the EI system in one place and they are getting some information about one way of doing it then they pick up some other information from somewhere else but that place is talking about an entirely different way of doing the EI system! You can see how this often causes confusion and ends with results not being what they should be.
So once I understood there were all these different ways of doing the EI system how did I decide which way I was going to use? For me, it was simple… literally!
I chose the simplest method.
What makes this method the simplest?
I'll start by showing you my 'recipe' for my tank. This is what I will be dosing and how I will be dosing it.
I'll be adding the weeks Macro Nutrients all at once by simply adding all the dry powders to the tank water after the weekly water change. This starts the tank off for the week with a full dose of Macro Nutrients. This is commonly known as 'Front Loading' the Macro Nutrients.
I'll be dosing the Micro Nutrients on the other 6 days of the week by mixing up a dosing liquid from a trace element mix and then using my dosing pump to add the correct dose of that liquid to the tank water daily.
The amounts I will use for my tank are as follows:
Weekly Dry Dosing (Sunday after W/C):
Potassium Nitrate 17g
Monopotassium Phosphate 2g
Potassium Sulfate 14g
Magnesium Sulfate Hepta. 31g
Other 6 Days Micro Nutrient Liquid Dosing:
Solufeed Sodium Free TEC 12g dissolved in 250ml of tap water - dosing 10ml 6 days a week.
How do I get to those amounts? This is where the 'IFC Aquarium Fertilizer Calculator' comes in.
NOTE: When you first open the calculator editing will be disabled, you will need to enable editing in order to use the calculator.
You want to start on the 'TankAndDosing' tab at the bottom of the spreadsheet.
In the area marked 1 you need to enter your tanks water volume and the volume of your water change.
In the area marked 2 just enter all 1's as I have here. Basically these do not matter as we are not using the Macro Nutrient liquid dosing calculations because we are dry dosing them. You have to enter something though to get to the Micro Nutrient section.
In the area marked 3 enter the amounts for your Micro Nutrient liquid dosing. For me it is a 10ml daily dose from a 250ml container 6 times per week. I would recommend copying mine and then adjusting them if need be once you see how this all works.
When it comes to working out the size of your Micro Nutrient liquid dosing container it needs to hold enough liquid to dose your tank for 4 weeks. Much longer than this and you will run into mould issues. When the 4 weeks is up you just mix another 250ml up in the container and carry on dosing.
The amount of liquid also needs to be enough liquid to be able to dissolve all the Micro Nutrient powder. If there isn't enough water then some of the powder will not be fully dissolved. The calculator will help you work this out though, as you will see.
Next you need to enter the nutrients that are already available in your tap water from your local water authority water quality report (you'll have to use Google to find the latest one from your area). Once you have the report you enter the amounts into the spreadsheet under the 'Core Settings' tab at the bottom of the spreadsheet.
As you can see I have entered the figures from my water quality report in the area marked 4. In my water quality report there is no reading for some of the elements so they have been left blank. I am told it will make little difference so if those readings are missing from your report just leave them blank.
Next switch to the 'TargetCalculator' tab, this tab will help you work out how much of the powders you will need for the nutrients in order to reach a specific target.
In the area marked 5 you choose which fertiliser you want to reproduce, this decides your target levels for the nutrients. For me it is 'EI Dosing Mid', which is designed to meet the needs of 'Medium Light/Medium Energy' planted aquariums. There is also 'EI Dosing Low' designed for 'Low Light/Low Energy' planted aquariums and 'EI Dosing Full' designed for 'High Light/High Energy' planted aquariums. If you choose a different one to me know that your amounts will be different from mine and you will need more or less powders. For now I'd select the same one as me so you can at least follow the rest of this guide.
If you scroll further down the same page you will see this section.
In the area marked 6 enter a 1 in the column for each of the same chemicals that I have. This tells the calculator you want a 1 to 1 ratio of each of those chemicals to reach the same level of those nutrients as used in the 'EI Dosing Mid' fertiliser that you chose in the last step.
Once you have entered those then the column marked as 7 will show the grams you need to dose of each chemical powder. I was told to just round these numbers up or down to the nearest whole. As you can see in the column marked 7, this results in the following list for my Macro Nutrient dry dosing powders:
Potassium Nitrate 17g
Monopotassium Phosphate 2g
Potassium Sulfate 14g
Magnesium Sulfate Hepta. 31g
Remember you are dosing these as dry powders so all you need to do is measure out that weight of each powder and throw it in your tank water after you have finished your weekly water change.
In the area marked 8 you can select 'EI Dosing Mid' from the blue cells menu and the values for that fertiliser are then shown below that row whilst your amounts are shown above that row so you can compare them. As you can see mine are mostly spot on with the Calcium very slightly over, which won't make any real difference.
If you then scroll down to the bottom of the same page you see this section:
In the area marked 9 you select the 'Solufeed Sodium Free TEC' from that cells menu. 'Solufeed Sodium Free TEC' is the trace element mix that I am using. Once you have that selected the rest of the row will fill in.
In the column titled 'Solubility level in container volume' you should see a percentage, hopefully in green and below 100%. Mine shows 84% here. This is how much of the water volumes salt solubility level is being filled by the amount of powder you need to add to it. If this is over 100% and in red then you need to use a larger water volume in your dosing container to allow the powder to dissolve fully.
In the column titled 'Add to container (gram)' you will see the weight in grams that you need to add to the water in your dosing container. In mine you can see it says I need to add 11.81 grams. You can round this up to 12 grams.
Remember this is the amount you need to add to the volume of tap water you selected at the beginning, so for mine it is 12 grams being added to 250ml of tap water.
In the area marked 10 you can see that the iron (Fe) in your mix is being matched to the iron level in the 'EI Dosing Mid' fertiliser, in this case a level of 0.350 Fe.
That's all you need to do to work out what you need to dose the EI Fertiliser and it is how I got to the amounts I will be dosing that I showed you at the beginning.
If you can follow all that then you should be able to work out how you can adjust it to suit your own tank. You can choose to replicate the low or full EI fertiliser, instead of the mid one, and/or use a different size Micro Nutrient dosing container.
There are costing sections in the spreadsheet that originally helped you calculate the cost of the powders you need when ordered from a popular website at the time (many years ago now!) these calculations are now totally incorrect and are of no use, so you should just ignore them.
I buy all the dry Macro Nutrient powders from 'Aqua Plants Care' and the trace elements mix from Solufeed directly. If you are not in the UK then you may need to source the powders for yourself.
The 4 Macro Nutrient powders I need from 'Aqua Plants Care' currently cost £46.96 for over 6 months worth of 3 of them and over 2 years worth of the other one. Another 6 months worth of the first 3 will cost £36.97.
The Micro Nutrient trace element mix (Solufeed Sodium Free TEC) currently costs £22 for 1kg, which will last me almost 7 years!
As you can see the cost savings compared to commercial fertilisers is massive, especially when you consider how much more concentrated this fertiliser is.
Hopefully that helps somebody out when trying to get started with EI Fertiliser dosing. I know it took me a lot of time and questions to figure it all out and if this saves someone else having to do that then it was worth the time writing this all up.
Any questions feel free to ask.
I avoided using it because of the complexity and the amount of varying information that was available on the subject. I don't like to use anything that I don't understand and trying to understand the EI system was problematic so I left it alone in favour of using commercial fertilisers.
Only when it came to preparing for my current tank build did I decide that the time had come for me to get to grips with it. The large volume of water in my new tank meant that using commercial fertilisers was no longer financially viable. It would be way too expensive.
I set about learning the EI system and soon came across something called the 'IFC Aquarium Fertilizer Calculator'. This is an Excel based spreadsheet calculator written years ago by some very clever people from a UK based Aquatic Plant Forum.
I'd post a link but I don't want to advertise another forum here. If you Google 'IFC Aquarium Fertilizer Calculator' though you will certainly find it anyway.
It is this spreadsheet calculator that is critical in working out your own 'recipe' for the EI Fertiliser system. I will be posting screenshots of the values I have entered into the spreadsheet to show you how I got to the amounts I use for dosing, so if you want to follow along or try this for yourself then you will need to download the 'IFC Aquarium Fertilizer Calculator'. The current version (as I write this) is v1.3.1 and this is the version I have used.
When it comes to the EI fertiliser system there are multiple ways to create the mixture(s) that you dose to your tank as well as multiple different ways of actually dosing. This is what makes the EI system so confusing, I think anyway. It took me a while, and a lot of questions, to finally figure out what was going on.
I'm not going to go into the details of all the different ways that you can do the EI system, suffice for you to know that there are multiple ways and all of them work just as well. Different people use the different ways, either through preference or belief that a particular way is 'better' for them. No one way has had more success than any other though, they all work just fine. If you want to look more into any of the other ways, or would like even more technical details, then I would suggest reading all the information on the forum where the 'IFC Aquarium Fertilizer Calculator' comes from.
Because there are all the different ways to do EI Fertiliser they have become mixed up and misunderstood. For example, people read about the EI system in one place and they are getting some information about one way of doing it then they pick up some other information from somewhere else but that place is talking about an entirely different way of doing the EI system! You can see how this often causes confusion and ends with results not being what they should be.
So once I understood there were all these different ways of doing the EI system how did I decide which way I was going to use? For me, it was simple… literally!

What makes this method the simplest?
- You don't need to make up a liquid to dose the Macro Nutrients at all, so no dosing pump required for Macros.
- You just add the dry Macro Nutrients once a week.
- The Micro Nutrient liquid is made from just one powder, you don't have to measure/mix separate powders.
- The steps needed to work out what you need in the calculator are relatively simple to follow and easily repeatable.
I'll start by showing you my 'recipe' for my tank. This is what I will be dosing and how I will be dosing it.
I'll be adding the weeks Macro Nutrients all at once by simply adding all the dry powders to the tank water after the weekly water change. This starts the tank off for the week with a full dose of Macro Nutrients. This is commonly known as 'Front Loading' the Macro Nutrients.
I'll be dosing the Micro Nutrients on the other 6 days of the week by mixing up a dosing liquid from a trace element mix and then using my dosing pump to add the correct dose of that liquid to the tank water daily.
The amounts I will use for my tank are as follows:
Weekly Dry Dosing (Sunday after W/C):
Potassium Nitrate 17g
Monopotassium Phosphate 2g
Potassium Sulfate 14g
Magnesium Sulfate Hepta. 31g
Other 6 Days Micro Nutrient Liquid Dosing:
Solufeed Sodium Free TEC 12g dissolved in 250ml of tap water - dosing 10ml 6 days a week.
How do I get to those amounts? This is where the 'IFC Aquarium Fertilizer Calculator' comes in.
NOTE: When you first open the calculator editing will be disabled, you will need to enable editing in order to use the calculator.
You want to start on the 'TankAndDosing' tab at the bottom of the spreadsheet.
In the area marked 1 you need to enter your tanks water volume and the volume of your water change.
In the area marked 2 just enter all 1's as I have here. Basically these do not matter as we are not using the Macro Nutrient liquid dosing calculations because we are dry dosing them. You have to enter something though to get to the Micro Nutrient section.
In the area marked 3 enter the amounts for your Micro Nutrient liquid dosing. For me it is a 10ml daily dose from a 250ml container 6 times per week. I would recommend copying mine and then adjusting them if need be once you see how this all works.
When it comes to working out the size of your Micro Nutrient liquid dosing container it needs to hold enough liquid to dose your tank for 4 weeks. Much longer than this and you will run into mould issues. When the 4 weeks is up you just mix another 250ml up in the container and carry on dosing.
The amount of liquid also needs to be enough liquid to be able to dissolve all the Micro Nutrient powder. If there isn't enough water then some of the powder will not be fully dissolved. The calculator will help you work this out though, as you will see.
Next you need to enter the nutrients that are already available in your tap water from your local water authority water quality report (you'll have to use Google to find the latest one from your area). Once you have the report you enter the amounts into the spreadsheet under the 'Core Settings' tab at the bottom of the spreadsheet.
As you can see I have entered the figures from my water quality report in the area marked 4. In my water quality report there is no reading for some of the elements so they have been left blank. I am told it will make little difference so if those readings are missing from your report just leave them blank.
Next switch to the 'TargetCalculator' tab, this tab will help you work out how much of the powders you will need for the nutrients in order to reach a specific target.
In the area marked 5 you choose which fertiliser you want to reproduce, this decides your target levels for the nutrients. For me it is 'EI Dosing Mid', which is designed to meet the needs of 'Medium Light/Medium Energy' planted aquariums. There is also 'EI Dosing Low' designed for 'Low Light/Low Energy' planted aquariums and 'EI Dosing Full' designed for 'High Light/High Energy' planted aquariums. If you choose a different one to me know that your amounts will be different from mine and you will need more or less powders. For now I'd select the same one as me so you can at least follow the rest of this guide.
If you scroll further down the same page you will see this section.
In the area marked 6 enter a 1 in the column for each of the same chemicals that I have. This tells the calculator you want a 1 to 1 ratio of each of those chemicals to reach the same level of those nutrients as used in the 'EI Dosing Mid' fertiliser that you chose in the last step.
Once you have entered those then the column marked as 7 will show the grams you need to dose of each chemical powder. I was told to just round these numbers up or down to the nearest whole. As you can see in the column marked 7, this results in the following list for my Macro Nutrient dry dosing powders:
Potassium Nitrate 17g
Monopotassium Phosphate 2g
Potassium Sulfate 14g
Magnesium Sulfate Hepta. 31g
Remember you are dosing these as dry powders so all you need to do is measure out that weight of each powder and throw it in your tank water after you have finished your weekly water change.
In the area marked 8 you can select 'EI Dosing Mid' from the blue cells menu and the values for that fertiliser are then shown below that row whilst your amounts are shown above that row so you can compare them. As you can see mine are mostly spot on with the Calcium very slightly over, which won't make any real difference.
If you then scroll down to the bottom of the same page you see this section:
In the area marked 9 you select the 'Solufeed Sodium Free TEC' from that cells menu. 'Solufeed Sodium Free TEC' is the trace element mix that I am using. Once you have that selected the rest of the row will fill in.
In the column titled 'Solubility level in container volume' you should see a percentage, hopefully in green and below 100%. Mine shows 84% here. This is how much of the water volumes salt solubility level is being filled by the amount of powder you need to add to it. If this is over 100% and in red then you need to use a larger water volume in your dosing container to allow the powder to dissolve fully.
In the column titled 'Add to container (gram)' you will see the weight in grams that you need to add to the water in your dosing container. In mine you can see it says I need to add 11.81 grams. You can round this up to 12 grams.
Remember this is the amount you need to add to the volume of tap water you selected at the beginning, so for mine it is 12 grams being added to 250ml of tap water.
In the area marked 10 you can see that the iron (Fe) in your mix is being matched to the iron level in the 'EI Dosing Mid' fertiliser, in this case a level of 0.350 Fe.
That's all you need to do to work out what you need to dose the EI Fertiliser and it is how I got to the amounts I will be dosing that I showed you at the beginning.
If you can follow all that then you should be able to work out how you can adjust it to suit your own tank. You can choose to replicate the low or full EI fertiliser, instead of the mid one, and/or use a different size Micro Nutrient dosing container.
There are costing sections in the spreadsheet that originally helped you calculate the cost of the powders you need when ordered from a popular website at the time (many years ago now!) these calculations are now totally incorrect and are of no use, so you should just ignore them.
I buy all the dry Macro Nutrient powders from 'Aqua Plants Care' and the trace elements mix from Solufeed directly. If you are not in the UK then you may need to source the powders for yourself.
The 4 Macro Nutrient powders I need from 'Aqua Plants Care' currently cost £46.96 for over 6 months worth of 3 of them and over 2 years worth of the other one. Another 6 months worth of the first 3 will cost £36.97.
The Micro Nutrient trace element mix (Solufeed Sodium Free TEC) currently costs £22 for 1kg, which will last me almost 7 years!

As you can see the cost savings compared to commercial fertilisers is massive, especially when you consider how much more concentrated this fertiliser is.
Hopefully that helps somebody out when trying to get started with EI Fertiliser dosing. I know it took me a lot of time and questions to figure it all out and if this saves someone else having to do that then it was worth the time writing this all up.
Any questions feel free to ask.

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