Originally Posted by Loyal to the Oil
The thing that bugs me about EI is this (keep in mind im new so i dont know much haha).
For example sake....if i dose say 2 parts KNO3 throughout a week. Then do 50 % water change and add 2 parts the next week again. I could hypothetically have 3 parts NO3 in the tank if the plants didnt use any up. Then the next week do 50 % WC and i could have 3.5 parts NO3 in the tank. Then the next week i could have 3.75 parts etc etc etc....
In the tom barr report he says you cant get more than twice what you are dosing built up in your tank but thats just not true by my figuring....
Eventually over time if you are dosing even slightly more of any nutrient than the plants are using up then you will eventually have sky high concentrations of this parameter in your tank ! So if you arent EVER testing then this IS NOT a far fetched situation and that could cause hell in the tank !
Where is my thinking wrong ?
With that explanation, why don't all fish only aquariums build up their PO4/NO4 indefinitely then?
There's no uptake right and you keep adding a source of NO3....?
Why don;t they keep building up?
You are removing a fraction of the build up as well each week, not just 50% of what you have added.
This is explained mathamtically in an "infinite series".
From the APD:
"If you assume that nothing is consumed, and you dose the same amount each week (X), and you change 50% of the water each week...
Week 1 = X
Week 2 = X + X/2
Week 3 = X + X/2 + X/4
Week 4 = X + x/2 + x/4 + x/8
This is a simple series:
/__ 2 where n goes from 0 to infinity
It converges at 2. To find the maximum concentration multiply X times 2. So at a large number of weeks then you can safely say that the concentration after 50% water change + X is equal to 2X. Doesn't matter if it's KNO3 or fish poop or some allelopathic substance excreted by plants. If you are doing a 50% water change every 4 weeks but are dosing X each week then at the end of a sufficient number of months the maximum concentration of X is 2(4X) or 8X. You can set up a series for any dosing and dilution scheme. Some of them "converge" or have a maximum value. Some don't.
A 10% water change weekly and dosing X gives:
X+.9X+.81X+ .729X which builds up concentration pretty fast."
As you can see, a 50% weekly water changes converges at 2x the weekly dose.
So adding 20ppm of KNO3 every week means it'll never go beyond 40ppm.
Don't like that wide a range?
Try 75% Weekly water changes
That will narrow it between the weekly dosed and possible build up.
50% is just an example and one that works well.
If you did not do but a 10% weekly water change and added 10ppm NO3, run the 10% build up series above..........
Yes, I am asking to use math to show and prove it to your self
While not 2+2 = 4 level, it's still pretty clear.
I think many folks are under this illusion, initially I was as well but knew that it could not be right as fish only tanks without any plants had no build up or uptake of NO3 that got good water changes and high very high bioloads.
There is a % of the remainder of the old water that gets removed each time a a new water change is done.
That's the part that gets removed and why the levels of NO3 etc never build up.
This also assumes no NO3 in the tap.A call to the water dept will quickly let you know, say you have an infant and need to know for health reasons, they will snap to fast.