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Discussion Starter · #1 · (Edited)
Hi guys,

I know many guys here have years of experience keeping planted tanks and over the years have experimented with different fertilizing methods.

So my question is in your experience what is a good estimate for the ratio of usage of different macro and micro nutrients. Please note that I am not referring to the ratio that you should keep in your tank, which is for example phosphate should be kept around 0.5 to 1 ppm and nitrate between 10 ppm and 20 ppm and so on. rather I am referring to how much your tanks actually use. for example, if you tested phosphate on yesterday and today and it dropped from 1 ppm to 0.6 ppm you would work out that around 0.4 ppm phosphate was used daily.

So can you say, for example, that N is used 6x P or iron is used 0.1 N and so on? if so, what are the ratios that you've found?
 

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The average ratio plants use nutrients in is: 106 C:16 N:1 P:0.1-0.001 Fe. So if 0.1 ppm of P is used 10.6 ppm carbon is used. You only need to check all sources of C N P etc that are in the water. Calculate all CNP etc that goes in the tank by food etc.
Also keep in mind that for example if your PO4 is 0.4 ppm lower, some might have been used by plants but some might as well be bound to the substrate or formed a complex with iron etc. Different plants have different ratios as well.

Personally I found for example that my fern dominated tank uses more PO4:NO3 compared to tanks with fast growing plants like glosso. But for a mixed tank it is a good start.
 

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So can you say, for example, that N is used 6x P or iron is used 0.1 N and so on? if so, what are the ratios that you've found?
Unfortunately there are no hard and fast ratios of this many N's to this many P's or any other similar pattern between other nutrients in our aquariums that every plant obeys.

Uptake of each nutrient depends on a large number of factors that are constantly changing. Each species has a given preference and minimum uptake requirement for each nutrient. Each plant can store nutrients for later use, taking them up even when they aren't using them (luxury uptake), or use them right away.

The amount of light a plant gets per day, hour, minute also affects uptake of each nutrient. As plants grow they shade each other and grow at different rates, this changes their nutrient requirements. As they grow older they develop different sized root systems to green tissue (different types of tissue require different ratios of nutrients). Some species of plants can poison other species and slow down their growth rate, block a specific nutrient from being used, etc. Not to mention all the other creatures in the tank that use the same nutrients (bacteria/fungi/etc). The list goes on and on.

While all of these factors are constantly changing we do know what unlimiting conditions are for most people's tanks. This is what the fertilizing system of EI (estimative index) is based on - providing more nutrients than plants are likely to need and preventing them from running out of any one of them and developing deficiencies.
 

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Discussion Starter · #4 · (Edited)
both responses are very informative and give lots of clues, thanks a lot.

I gather that there are too many variables-like plant species, substrate, life stages of all plants, microorganisms, lighting, chemical reactions, etc- to make a general rule that applies perfectly to all tanks and only a rough estimate can be given.

As Zapins said this explains the philosophy of EI. But with EI there is a logical doubt, at least in the minds of beginners like me, that if you constantly overdose and don't check parameters you'll end up poisoning or causing algae outbreaks.

So is it fair to say that we can get the concept of providing excess nutrients from EI but modify EI, meaning we test water parameters to make sure we are not grossly off limits?
 

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As Zapins said this explains the philosophy of EI. But with EI there is a logical doubt, at least in the minds of beginners like me, that if you constantly overdose and don't check parameters you'll end up poisoning or causing algae outbreaks.

So is it fair to say that we can get the concept of providing excess nutrients from EI but modify EI, meaning we test water parameters to make sure we are not grossly off limits?
By doing 50% water changes every week, essential with normal EI, it is mathematical impossible to get a build up of nutrients high enough to poison anything.
 

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I see where you are coming from.

The thing with EI is that it relies on frequent large water changes to flush out any build up.

So if we assume plants use none of the nutrients you are adding and you are adding 10 ppm of something each week while also doing 50% water changes. What happens is:

1st week: Start with 10 ppm, 50% water change, now you are at 5 ppm.
2ndweek: 10+5 ppm, do a 50% water change now you are at 7.5 ppm.
3rdweek: 10+7.5 = 17.5, half 8.75
4th week: 10+8.75, half 9.375
5th week: 10+ 9.375, half 9.6875
6th week: 10+9.6875, half 9.84375
Many weeks later 10+10, half is 10
Many weeks later 10+10, half is 10
Many weeks later 10+10, half is 10
etc etc until you reach a maximum concentration of 20 ppm after several weeks of following this pattern.

So basically if you follow the EI directions and do weekly 50% water changes, you will only ever be able to achieve twice the weekly dose. It will never accumulate past this.

If you do 75%, or 25% water changes then the same sort of thing happens but you flat line out at a higher or lower ppm value.

There is a nice calculator that wet made a while back what allows you to see what happens over the long term. It graphs out the concentration of nutrients vs. time and allows you to check what happens if plants use up a certain amount per day or don't use any up: http://rota.la/ei/

This is why EI works so nicely. You can certainly test the water parameters if you like, but it usually isn't necessary or very helpful.
 

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Discussion Starter · #7 ·
By doing 50% water changes every week, essential with normal EI, it is mathematical impossible to get a build up of nutrients high enough to poison anything.
Thanks for the clarification.

There is a nice calculator that wet made a while back what allows you to see what happens over the long term. It graphs out the concentration of nutrients vs. time and allows you to check what happens if plants use up a certain amount per day or don't use any up: http://rota.la/ei/
Great page, a little playing with the numbers gives a good understanding of effects of dosing and WC.
 
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