Kinda confused on EI - please validate my dosing


Lifetime Charter Member
Lifetime Member
Mar 3, 2007

Thanks in advance for anyone willing to look through this, it will really help me a lot to get some feedback.

Please help me validate not only my EI dosing strategy, but my logic of how I got there. Each time I sit down to figure out what I should be dosing I admit to getting a bit confused, despite reading gazillions of posts on the same topic.

Here is my step-by-step (so you can see my logic and math) for how I plan to dose my 20gal tank, non-co2 with Excel; about 2wpg.

STEP 1: identify standard EI dosing
From general EI dosing:
General Dosing Guideline for High Light and well planted aquariums.
10- 20 Gallon Aquariums
+/- 1/8 tsp KNO3 (N) 3x a week
+/- 1/32 tsp KH2PO4 (P) 3x a week
+/- 1/32 tsp K2SO4 (K) 3x a week
+/- 1/32 tsp (2ml) Trace Elements 3x a week

STEP 2: use dosing calculator to see what that means in added ppm
From Chuck Gadd’s calculator:
1/8 tsp (.73g) dry KNO3 to 20gal adds +5.89 ppm nitrate
1/32 tsp (.14g) dry KH2PO4 to 20gal adds +1.29 ppm phosphate
1/32 tsp (.14g) dry K2SO4 to 20gal adds +.83 ppm potassium

STEP 3: establish new ppm target because my tanks is non-co2
Since I have a non-co2 tank, I choose 65% of full EI dosing as the “new target ppm”
So Gadd ppm from full EI X .65 = new target ppm
+5.89 ppm nitrate X .65 = 3.83 = new nitrate target ppm
+1.29 ppm phosphate X .65 = .84 = new phosphate target ppm
+.83 ppm potassium X .65 = .54 = new potassium target ppm

I want to make stock solutions in 500ml distilled water containers
The cap of my containers is 5ml, and I want to add 5ml of the solution each time I dose
(for convenience, so I always only add one cap)

By trial and error I bumble around with the Gadd calculator for mixing solution in 500ml until the added ppm in 1ml is 1/5 of my new target value – so that 5ml (1 cap full) of the mixed solution will = my new target ppm value for that solution when I dose

STEP 4: figure how much dry to add to 500ml so 5ml of solution will add my desired new target ppm
Though trial and error, Gadd calculator shows
48.0g dry KNO3 in 500ml adds +.77 ppm nitrate with each 1ml mixed solution
(.77 x 5ml = +3.85 nitrate)
9.0g dry KH2PO4 in 500ml adds +.17 ppm posphate with each 1ml mixed solution
(.17 x 5ml = +.85 phosphate)
9.0g dry K2SO4 in 500ml adds +.11 ppm potassium with each 1ml mixed solution
(.11 x 5ml = +.55 potassium)

STEP 5: hope I did it right
I will dose 1-2x per week
Each time I dose I will add 5ml of each solution
So each time I dose I will be adding
+3.85 ppm nitrate
+.85 ppm phosphate
+.55 ppm potassium