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Jeff Kropp, 60g, March 2005

Aquarium fertilizer dosing guide

The dosing instructions for many of the fertilizers on our website can be located either in the FAQ's or the "more information" section for each individual fertilizer in the web store.

There are also many aquatic plant forums and blogs where you can find information and advice.  Or you can download Greg Watson's Guide to Dosing Strategies which can be found online at  www.aquaticplantnews.com for only $4.95. This is an excellent resource guide on how to keep planted aquariums. The proceeds from the sale of this guide go toward supporting the hobby through various clubs and forums.


Information about how to use and how much to use of the fertilizers you purchase at AquariumFertilizer.com is also available at The Barr Report, www.barrreport.com.  With permission from Tom Barr, we have reprinted some of the information here:


From the Barr Report at www.barrreport.com


Confusion about EI and other myths

As this method has become popular, it also has had growth pains.

1. It was never meant to be applied rigidly.

2. It is a simple concept, provide non limiting nutrients without having to test to do so.

3. Adding non limiting nutrients provides the plants with optimal nutrients so folks can rule out deficiencies 4. Precise plant nutrient Deficiencies are not known for most every aquatic plant. This requires a high level of testing and things like fish food, sediments and other potential confounding factors come into play.

5. If you have lower growth, lower light, then you can make safe assumptions like using less nutrients, again, refer to #1.

6. Algae are not nutrient limited in aquariums with fish and plants. 

Argue this all you want, but you need to research and see what types of nutrient levels will limit algae. They are extremely low and any fish waste and plant decay, leaching etc is more than enough to supply algae with all they need.

7. 90-95% of all algae related issues are due to improper use of CO2.

8. 90-95% of all algae problems are related to improper use of CO2. 

There is a good reason to repeat this because folks will forget and blame the nutrient dosing method(and this issue is not limited to just EI, every other dosing routine has the same issues).

9. Measuring CO2 carefully is not easy. It varies, it's influenced by circulation a great deal, it can change 10X in concentration in less than 30-45 minutes.

No other nutrient can change this rapidly, nor is critical to every other nutrient. Algae take advantage of this variation to germinate and establish.

Be very careful in assuming you are 110% positive you have enough, instead, rule out everything else first, then go about tweaking CO2 and do so slowly, never rush or get impatient.

10. In general, less light is better than more for every method using CO2. This reduces CO2 demand, if you use higher light, consider having methods to reduce it, control it if any issue come up.

11. EI rules out nutrient deficiencies. While this can rule them out, many find that after adding non limiting nutrients, they still have issues. EI is not solely about nutrients, if the CO2 demand was limited because there was not much PO4, now the CO2 demand is greatly increased. 

If the CO2 is not also increased to account for this change, then it can lead an aquarists to incorrectly assume that it is the PO4 that is causing the plant or algae issue. However, it is a secondary effect. If the CO2 was controlled correctly in the test, then the algae/plant issue would not have occurred. Such error/s in logic cam lead to false assumptions/conclusions.

12. Make as safe assumptions as you can.

13. Test if you want along with EI. Some do so to get a feel for their aquarium, then no longer test if they are within the target(theirs or EI's etc) ranges. These are choices you make/trade offs and you decide if they are worthwhile for you.

There is no rule that says you cannot test. I suggested testing along with water changes in the past(see 1996-1997 list of levels of parameters thread here). However, testing correctly is not been one of aquarist best traits These are cheap test kits and with poor resolution, so it is wise to calibrate any test kit before relying on any data obtained from their results. Even 10,000$ lab test equipment is calibrated, this way we know the results are accurate.

14. EI is not based on flowery language, perception or marketing schemes. It is not based on faith. It does not disparage other methods. 

The results are testable, the concept come from PMDD and the math is even in there as well, I simply posed a few graphs.

15. EI is specific to the water column source of nutrients, however water does diffuse into sediments and can become a source of nutrients to the roots as well. This does not preclude aquarist from using root sediment sources as well in conjunction with water column fertilizers.

16. Ratios. Hot topic and few really understand anything about it and why it does not matter. Epstein and Bloom are two very well respected researchers on this topic and it really gets down to limiting vs non limiting levels much more than a ratio (see their text: Mineral nutrition of Plants, Principles and Perspectives, 2005). Ratios can save the farmer spending 1000$ on fertilizers and reduce their runoff waste, however, aquarist do not have issues here and the cost is insignificant. 

Still, a relative range of ratios is not bad either, but with the wide range of species kept and each one having their own set of growth rates, nutrient demands, this seems very difficult to apply in a general way.

17. RR or Redfield ratio, often discussed and cited and folks make a mistake in mass vs atomic number of atoms. A ratio of atoms, number, is

1 P for each N according to marine algae in Redfield's paper. This is not mass.

P is 30.97 grams per mole

N is 14.01 grams per moles

To convert to mass, you need to multiply N by 2.2, now the RR is 7:2 1, or about 10:1 for NO3/PO4.

Still, this is just what is available from upwelling in ocean systems and is typically under extremely high light, full sun etc. The system becomes limiting after prolonged algae growth. This is radically different from what occurs in freshwater systems where aquatic plants are involved. Fresh water plants have different ratios, different nutrient sources and cycling, as well as being able to concentrate nutrients from their external surroundings at a much high gradient internally.

18. Inhibiting levels of nutrients, the upper bounds. Generally, this is from osmotic conditions, too much salt basically. Hoagland's modified solution is very rich and is a non limiting nutrient solution. EI is just a similar idea but on the lower end for aquatic plants, above the limiting ranges but not nearly as rich. Hydroponics and Hoaglands solution has a very long history and test/research background for support. EI is no where even remotely close to these levels of inhibition.

19. Less light = less demand for nutrients. You can go too far and get so low plants will not grow no matter what the CO2/nutrients, however, it's a very useful way to control the rates of growth for an aquarium and also to control algae until the conditions are corrected. Many have issues with CO2, so using less light makes targeting a good stable CO2 level much easier than say higher light intensity. Thus limiting light makes the most logical sense, not nutrients and CO2 for algae control, for stability, for CO2 issues/nutrient issues, for control of growth rates, for less electrical use, reducing heat, reduction of any and all waste.

20. If the CO2 is not properly added, then EI, nor most any method(unless it limits a nutrient so much that CO2 decreases) will help you. Severely limiting PO4 can reduce CO2 demand, but can be difficult to keep doing. Might as well just use less light, since that's where all growth starts. You see? Lots of CO2 talk, very little about nutrients............

21. It is an INDEX, any index simplifies reality, thus has inherent limitations like any index or indices, such as the stock market, economic forecasting or species diversity. Any attempt to compress complex data into a single index will suffer some loss of information.

that's why I chose to refer to it as EI, not something cheesy like Tom's wonderful magic potion of plant growth. This index is fairly robust because of what went into the general concept, it assumed the highest possible rates of growth at the upper limit. So we will essentially never run out of any fertilizer. EI does not nor any other nutrient method done much with CO2 or light(EI just used an upper possible bound with respect to light) So if you mess up CO2, which most/many aquarist do at some point(either application or measurement errors, assumptions), then algae, or poor results are not independent of light and CO2, they become dependent.

A nutrient method cannot be judged unless those other two main players in plant growth and fully addressed, this has long lead to confusion and blame.

Most hobbyist just want good plant growth and no algae issues. They rarely do test to illustrate and confirm independence in such test systems and experiments. A good way to do it: have a nice tank without algae and good growth of plants. That makes the best control for falsifying something, but will not tell you what something might be with certainly.


Regards, Tom Barr






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