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Estimative Index Dosing Guide

469561 Views 224 Replies 99 Participants Last post by  mistergreen
The Estimative Index (EI) coined by Tom Barr 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 to out compete algae growth.

The process of which this is done is simple. Each day 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). 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 schedule is repeated.

The primary fertilizers are the macro nutrients - Nitrogen (N), Phosphorous (P), Potassium (K), and the micro nutrients - trace elements (Plantex CSM+B, Flourish). 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 lower light setups, smaller quantities of fertilizers should be dosed in those instances.

General Dosing Guideline for High Light and Well Planted Aquariums

10- 20 Gallon Aquariums
+/- 1/8 tsp KN03 (N) 3x a week
+/- 1/32 tsp KH2P04 (P) 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 (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 (10ml) Trace Elements 3x a week
50% weekly water change

60 - 80 Gallon Aquariums
+/- 3/4 tsp KN03 3x a week
+/- ¼ tsp KH2P04 3x a week
+/- ¼ tsp (20ml) Trace Elements 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 (30ml) Trace Elements 3x a week
50% weekly water change

Note: K2SO4 is not required for dosing unless you need the extra Potassium (K). This K is found in KN03 and KH2P04. Dosing these two according to above will yield sufficient K levels. Therefore, one will be fine dosing only KN03 and KH2P04, and Plantex. If one needs to increase their K levels with K2S04, add the same measured amount as KH2P04. For example, if one is dosing 1/2 tsp of KH2P04, then dose 1/2 tsp of K2S04. In true regards to EI, added excess K is not detrimental in any event.

EI target ranges
CO2 range 25-30 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

Where to buy fertilizers?
AquariumFertilizers. com could have provide you with the necessary chemicals for dry and liquid dosing of the above but is out of buisness. For micro - trace elements, Plantex CSM+B, Seachem Flourish, and Tropica AquaCare are equivalent to each other. Drsfostersmith and bigalsonline for the Seachem and Tropica brands.

One Pound of each of Aquarium Fertilizer/Greg Watson's Chemicals will last at least 1 year:
Plantex CSM+B​
Potassium Nitrate KN03​
Monopotassium Phosphate KH2P04​
Potassium Sulphate K2S04 (optional)

Special Notes:

Providing optimal CO2 levels of at least 30 ppm are necessary for plants to prosper and out-compete algae. 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 dosing straight into the tank, or they dissolve each chemical in water before adding.

Making a Liquid Stock of Plantex CSM+B is more often mixed into a bulk liquid solution since some find it more convenient to dose their trace elements this way. The recipe for this solution is 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.

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.

Stick to a good dosing regime and your plants will flourish!
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Great overview! I'm sure I'll be referencing this thread often . . . . very simple to understand. I especially like the target levels and the dosing schedule table!
just wanted to ask, I see that you added doseing of K2SO4, where on the barrreport Tom doesnt recomend that, and says that in most all cases you get more than enough K from the KNO3.

I have been doing EI for a while now, and have checked CO2 over... and over.... and over again..... I have tried MANY different ratios of this and that which are supposed to be best.... with still less than desirable outcome. Fianally after reading through some other post and looking at the history of problems I have had, which have been the same all through this time of trying different ratios of Ca to Mg and adding more Iron than should ever be needed to try to get new growth to come in a nice green. I decided that maybe.... just maybe I didnt have enough K and that was my problem. So i started adding more 3x a week similar to what you have suggested.

This was a few days ago and its still to soon to tell if this is going to help things at alll but I am excited to see if maybe I have fianally gotten to the bottom of things and can start growing healthy plants. So i was just curious to see the reason behind recomending the extra dose of K2SO4? have you found that in some situations K from KNO3 to not be enough?
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Excellent overview!

I'd just like to add a point about the water changes/resetting the tank. If you change 50% of your water once a week, you will *never* have more than a maximum of twice your weekly dosing of fertilizers. And that's without taking into account plant uptake.

For example, if you dose 3mg/l (ppm) of NO3 a day, or 21mg/l a week, your NO3 levels should never reach more that a maximum of 42mg/l. Add in what the plants can use up and the amount will be lower. If they do go above the 42mg/l in this example, you don't have enough light/CO2/plants or you're overstocked with fish.

So obviously if you change less than 50% of the water once a week, or wait longer between water changes, the "reset" aspect will vary and you should adjust your dosing accordingly. I think that the dosages recommend above are based on 50% water changes...
Thank you John! Very nice summary of where to start with EI doses. This has been needed in a concise format for quite some time.

People should realize that there are situations where the above doses may need to be modified. These might include (but are not limitted to) higher than normal levels of nitrates or phosphates in your tap water, a very heavily stocked tank - especially with heavy feedings, or if you routinely go longer than a week between water changes.

The above methods were developed for high-light, CO2 supplemented systems as John mentioned. Low-light or non-CO2 setups are MUCH less likely to become nutrient limited and you can get away with smaller doses and go longer between water changes.

Also, many people feel that a supplemental iron source is sometimes required, depending on the exact composition of your micros.
This is just one routine, it's not written in stone.

You can use less in many cases, you can dose 2x a week in some cases, some dose daily, some do water changes over long time frame, say once every 2 weeks, some do smaller water changes(the trade off is more possible build up/more deficiency potentially), some larger(better stability to the pre set dosings).

Adding K2SO4 will not hurt, but there might be some other factor involved besides K+ alone.

You can leave it, I have not used K2SO4 as a part of a routine for several years now, few would say my plants/tanks have K+ related issues in any way.

But I think it's unlikely the low K+ had any nbearing unless there was not enough KNO3 being added.

Tom Barr
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Here is one excel sheet that shows concentration during EI usage with simple graph and estimative part. You can change dosing amouts to see "what will happen if ..."

(It's not that sheet I posted last time, this sheet is much simpler.)


sorry if this is obvious but this is for dry dosing correct?

10- 20 Gallon Aquariums
+/- 1/8 tsp KN03 (N) 3x a week
+/- 1/32 tsp KH2P04 (P) 3x a week
+/- 1/32 tsp (2ml) Trace Elements 3x a week
50% weekly water change
That's correct, the measurements are made for dry dosing in teaspoons as described in the article. For liquid dosing of NPK, see the link provided above in the special notes section regarding liquid solutions. There is no difference either way in dosing methods; it's what is most comfortable and convenient for the user.

-John N.
quoted from rexgriggs site
what problems does that cause and when should each be dosed if you cant mix it?
Actually, KNO3 and KH2PO4 won't cause any problems. What you need to avoid are mixing KH2PO4 and your iron (Fe) source. The two will precipitate out in some cases.

Are you sure you saw that on Rex's site? I didn't find that phrase on there.
Precipitate: KH2PO4 and Iron

Mike is correct,

  • Adding KNO3 and KH2PO4 together will not cause problems. The above statement is mistaken when dosing in large bodies of water such as an aquarium. In small containers you might have an issue.
  • Adding KH2PO4 and Fe (from traces) can cause a precipitate (white powder) to come out of solution. This chelated iron precipitate is now no longer available to the water column, and must now be taken up from the roots where the powder will settle.
  • Mixing macro elements and trace elements in the same bottle forms a highly concentrated and volatile solution of chemicals in a small amount of water (500ml). This could result in precipitation, cloudy and ineffective mixtures. That's why we shouldn't mix the chemicals together in a small container.
Bottom line with dosing together: When dosing the chemicals (macro and micro) in our aquariums together, you won't have a problem because they are now in a very diluted solution. However to prevent any precipitation (cloudiness), we can dose macro and micros on off days so that each are consumed before the introduction of the other.

-John N.
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will it also precipitate when traces and iron is mixed with kno3?

I had time to see the fertilator and im still digesting some of it hehehe. Anyway. can i put mgso4 and caco3 every time i put the macro. Or i will dose it on a different occasion say once or twice a week? Just a newbie question.
Fe and KNO3 should be fine. As for MgSO4 and CaCO3, what are your goals? You should be fine adding it with water changes and that's it.
Wow this is a very good thread. Short and sweet and straight to the point.
here's a link to rex's site and its in bright red at the bottom where he states the above. Rex's Guide to Dosing Dry Ferts
Ahhh. Guess what I think he means there...

If you confuse KNO3 and KH2PO4, you can have problems. Basically you could end up with extremely high PO4 levels and next to no NO3. That would be a recipe for disaster as your tank gets completely unbalanced.
Or in other words, it's ok to mix them together, but don't mix them up. :)
Fe and KNO3 should be fine. As for MgSO4 and CaCO3, what are your goals? You should be fine adding it with water changes and that's it.
thanks man!
so you are not suppose to mix fe with kh2po4 but seachem's suggested dosing chart suggest dosing iron everyday.

wouldnt the seachem products have the same problem with mixing iron and phosphates?
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