Estimative index, confused about K levels

[jestes]

OK, so I downloaded Chuck's planted aquarium calculator to double check that I was dosing my tank properly. Using the figures for the EI index on a 55 gallon tank I found here: Estimative Index Dosing Guide - Fertilizing - Aquatic Plant Central I came up with the following values:

N: 8.25
Suggested target level: 5

P: 1.95
Suggested target level: 1

K: 7.68
Suggested target level: 20

I'm also adding potassium sulfate. Here's how I came up with the K figure: 5.21 from KNO3, 1.55 from K2SO4, and I'm guessing .97 from the KH2PO4. The calculator didn't have that one, but .97 was half of the phosphate, and there's 2X as much P as there is K in the KH2PO4.

So, the only thing I can come up with is maybe the calculator is wanting too much K in the tank. Don't plants want around a 8:8:1 ratio of NKP?

Sorry if this question has been covered already, but I'm just trying to make sure I understand everything here.

 

[mgamer20o0]

Aquatic Plant Central this is the one i use to calculate. i always see it as a range. with EI you dump plenty of ferts in the tank so you dont have to worry about it.

 

[timwag2001]

the info from tom barrs site is a little bit more clear. EI light: for those less techy folks - - Aquarium Plants

you'll notice that they dont dose k2so4. you get enough from kh2po4 and kno3.

and i agree with mgamer. i think the apc site has the best calculator

 

[Purrbox]

Please note that Chuck's Calculator is suggesting target levels to maintain in an aquarium and is not in any way based on EI.

 

[jsoong]

One more point: Because K testing is expensive, it is not usually done. Experience had shown that excessive K (eg using water from a KCl ion-exchanger) has no bad effects on fish & plants, the normal routine in EI is to overdose on the K. Therefore, the K dosing is usually higher than the theoretical requirement. <Well, you have an over abundance of N & P as well .... that is why the 50% weekly pwc to reset things.>