EI and water changes ?

Davejt

Junior Poster
Dec 28, 2009
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I was wondering about the EI method - dose - dose - dose - water change out the surplus. Even with the water changes don't things still build up?

super simple example: say does 10 units of a nutrient and plants are using 5.

At the end of 1st week = 5 units left, 50% change.

2nd week starts with 2.5 units, dose 10 plants -5 leaves 7.5

50% change 3.75 units

3rd week does 10 = 13.75 units plants use 5 leaves 8.75

50% change = 4.4

4th week +10 = 14.4 - 5 =9.4

50% change = 4.7

Seems like they excess keeps climbing every week despite the 50% changes?

I must be missing something, or just over reacting, maybe over curious? or as time goes on does the amount added just become insignificant?

thanks
 

Biollante

Lifetime Charter Member
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Jun 21, 2009
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Water Changes-Good!

Hi,

Change more water if you wish. :D

I think we assume the plants and even the critters use some of the nutrients, some ends up in the substrate.

Biollante
 

Philosophos

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Mar 12, 2009
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The algorithm for EI with 20ppm of x nutrient as a weekly dose, without any external variables, would be as follows:

Week 1: 20ppm - 50% = 10ppm
Week 2: 10ppm + 20ppm -50% = 15ppm
Week 3: 15ppm + 20ppm -50% = 17.5ppm
Week 4: 17.5ppm + 20ppm -50% = 18.75ppm
Week 5: 18.75ppm + 20ppm -50% = 19.375
Week 6: 19.375ppm + 20ppm -50% = 19.6875
Week 7: 19.6875 + 20ppm -50% = 19.84375

In essence, you can never have more than the previous week's concentration plus the weekly dose as a maximum because of the 50% water change. Removing 50% of the water is like dividing by 2, and the quantity being added is never more than 20ppm.
 

Tom Barr

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Jan 23, 2005
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A partial amount of the prior week's remainder, it is removed.

Think about it, using the same logic you used, EVERY aquarium would build up with NO3 infinitely due to fish waste. This clearly does not happen right?

You can use the calculators to see the ppm's here:
http://wet.biggiantnerds.com/ei/con_v_time.pl

Just try adding say 10ppm NO3 3x a week and see what happens in the calculator.

Regards,
Tom Barr
 

Davejt

Junior Poster
Dec 28, 2009
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Philosophos;47463 said:
In essence, you can never have more than the previous week's concentration plus the weekly dose as a maximum because of the 50% water change. Removing 50% of the water is like dividing by 2, and the quantity being added is never more than 20ppm.

Ahh there it is... I knew there was a math reason... But been a long time since I used all of that stuff.

thank you!