Sometimes, it is easier to do a Google Search for things (such as Estimative Index) and get it straight from the source (Tom Barr's forum).
10- 20 Gallon Aquariums
+/- 1/8 tsp KNO3 (N) 3x a week
+/- 1/32 tsp KH2PO4 (P) 3x a week
+/- 1/4 tsp GH booster once a week(water change only)
+/- 1/32 tsp (2ml) Trace Elements 3x a week
50% weekly water change
The 2 mL volume is if you are mixing it up as a liquid. 1 teaspoon per 64 mL of water.
3 teaspoons = 1 tablespoon per 192 mL of water.
The 250 mL of water is slightly more dilute, but should work as well.
EI dosing was not meant to be extremely accurate.