Confusing eh? I've had this discussion before as some calculators seem to contradict each other. The E.I is a range and most seem to be the same just aiming for different targets. The range taken from UKAPS and most places to be fair are as follows.
Nitrate (NO3) 20ppm per week
Potassium (K) 30ppm per week
Phosphate (PO4) 3ppm per week
Magnesium (Mg) 10ppm per week
Iron (Fe) 0.5ppm per week
Now other calculators will aim for 30 ppm no3 to 20ppm and 1ppm to 3ppm po4 weekly. Checking
James planted tank that would suggest 0.186 grams in 100ltr tank for 1.3ppm dosed 3 times per week. As would
Rotala Butterfly same again 0.186=1.3ppm but says dose 2 or 4 times a week. So again they are aiming for a range of between 1/3ppm weekly. The only anomaly is
The Nutrient Company which for some reason seems to be trying to aim for 9ppm weekly! That's what blew my mind and I couldn't figure whether we were dealing with n or no3 or p or po4.
It's not exact science BTW, as Darrel mentioned plants consume mostly nitrate and potassium and the rest for a balanced diet. I assume 30ppm no3 and 3ppm po4 to be top of the shop unlimited with good flow. I then work my way down from there but at the same ratio. In my tank though I bear in mind that my tank creates it's own nitrogen from fish waste but not much po4 other than from fish food so I reckon the no3 will fall slower than the po4 in a well lit tank. Once you start rolling back if that's what you want to do at the top numbers there is enough potassium in both the kno3 and po4 but as these levels get lower you may need to add extra potassium in the form of potassium sulphate. Cross that bridge if you get to that.
I have a 500ml bottle mixed at the Nutrient company's recommendation of very high po4 which I gave up on, I may try and get my head around it later as it happens and see if I can mix a bottle which just kno3 in and combine the two.