Here is how I figured it out:
1) How many total gallons are you dosing? For me, add up all the gallons of all the tanks. For you, one tank @ 56 gallons is it.
2) Look at the EI recipe and figure out what 4 weeks worth of each fertilizer is.
40~60gal
50% H20 change-weekly
1/2 Tsp-KN03 3x a week~~ so a month's worth is 5.5 tsp
1/8 Tsp-KH2P04 3x a week~~so a month's worth is 1.5 tsp
Put that much in your bottle.
Next, what size syringe or turkey baster do you have? How many ml will you dose per day? Mine worked out to 1ml per 3gallons of tank size, so to get a months worth of doses for your tank (56 gallons) you would need about 20 ml per day x 12 days = 240 ml.
So put 240 ml of water in the bottle and shake well.
A similar reasoning works for whatever trace minerals you are using. Put a month's worth in the bottle. Put enough water in there for you to dose reasonably accurately 12 times. (dosing 3 days per week times 4 weeks per month is 12 doses).
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More of these chemicals can be dissolved in the water. Then you would dose less. For example, if you put 2 months worth in at a time, but kept the water at 240 ml, you would dose 10 ml each time. At some point you will find that you cannot dissolve more and more, it comes out of solution. Don't fight it, make a weaker solution and dose more.
I am using this method to mix and dose fertilizers for almost 1000 gallons worth of tanks.