Tom Barr's Method of Open Loop Aquarium

Tom Barr's Method Of Open Loop Aquarium Plant Fertilization
"Estimative Index"

In the late 1980's aquarium plant fertilization was in its infancy and there was scant information outside the Dupla book. Within years it seemed everybody had a plethora of test kits and "ppm" was the buzzword in aquatic plant fora all over the internet. But, Tom Barr makes a good point that you don't need the feedback from the (almost universally) inaccurate hobby test kits, you can simply change water and dose ad infinitum. Here is Tom's method, often called the "Barr method" (postscript a year later, I gues Tom is shy he refers to this as "estimative index" the term "Barr Method" didn't last), an answer to a question whether or not ones needs to be a chemist to dose aquarium plant fertilizers properly. I quote Tom directly:

Actually no, it's rather easy to determine the nutrient levels and maintain them in one simple step.

No chemistry lesson is needed at all; you can make cereal right? Add enough cereal to fill the bowl, add 2 cups of milk, 2 teaspoons of sugar.

Or I can say add 250 grams of endospermous carbohydrates and 9.5 grams of sucrose to 450mls of bovine lactate exudate.

In a nutshell, you do large weekly water changes (say 50%) each week to prevent anything from building up and and dose 2-4x a week to prevent anything from running out. The names can be whatever you want them to be, but ultimately all you are doing is adding Nitrate, PO4 , K+ (the NPK numbers of bags of fertilizer) and traces.

Farmers do this without chemistry lessons every day.

In this manner you provide a stable range of all the nutrients cheaply, easily and without using a test kit except for CO2(KH/pH).

An example routine for a 20 gal tank with high light:

50% water change

Add: 1/4 teaspoon of KNO3 1/16 or a smidge of KH2PO4 If GH is lower than 3-5 out of the tap, Add SeaChem Equlibrium(1/4 teaspoon)

Next day add 5 ml of trace

Wait one day, add the KNO3/KH2PO4 again, next day add the trace again

Add the KNO3/KH2PO4 Trace again the next day

Water change: repeat ad nauseum.

Dosing 1/4 teaspoon of powered KNO3 = 1.67 grams according to a lab scale with 10 levels averages.

This added to 20 gal= 10-11ppm of NO3. Error is about 1ppm of NO3.

Name one hobby kit that can be that accurate. I'm not aware of any.

We dose excess nutrients in all cases, and there is nothing wrong with that as long as we don't get too far off base; the water changes prevent folks from lousing it up.

You can guess estimate and use the plants as the indicator as you become more skilled and dose less or go longer without water changes. But again, no test kits are needed.

As long as you keep up on dosing and water changes, this is a very simple method and no hassle if you put an automatic water changer on your tank, python style water changer etc or hard plumb a drain/refill.

KH2PO4, KNO3 are very cheap, SeaChem Eq is relatively cheap as well for the once a week dosing. Traces are not too bad at this amount.