Ok.
Since we're getting technical, here's a sample calculation working with Grow More 10-20-30, where the ultimate goal is figuring out how much fertilizer to add to your stock solution(prior to injection) to achieve a desired PPM nitrogen in the FINISH solution, given a certain proportioner rate - existing tapwater N aside. Yes, I know Dosatron has an online calculator, but who cares
Say you want 100 PPM nitrogen in your FINISHED solution for a constant feed program, and the proportioner is set to a 1:50 ratio.
First, use that desired PPM N to find the amount of N present in 100 gallons of finish solution. Let's express everything in ounces by weight.
1 gal = 8.34lbs, So 8.34 x 16oz./lb = 133.44oz./gal, x 100gals. = 13,344oz.
100 gallons weighs 13,344oz. so use the following proportion:
If:
100oz. N
1,000,000oz. H20
Then:
x oz. N
13,344oz. H20
1,000,000x = 1,334,400
x = 1.334oz. N in 100gals. at 100PPM nitrogen
That's just nitrogen. We need to know how much fertilizer is in 100 gal, So:
Since 10-20-30 has 10%N, divide 1.334oz by 0.10 to get
13.34 oz. fertilizer in 100 gal
To get the amount of fert. for preparation of the stock solution, bear in mind that a 1:50 ratio means that 1 gal stock solution gets proportioned for every 50 gal water, producing 51 gal finished solution.
If:
13.34oz. fert
100 gals. finished
Then:
x oz. fert
51 gal finished
x = 6.80 oz. fert. in 51 gal finished solution
So, if 1 gal stock solution gets removed from the tank to make 51 gal finished solution, then you must dilute 6.80oz. of fert. for every gallon of stock solution.
Summary: 6.80oz. of 10-20-30/ gallon stock solution will produce a 100 PPM nitrogen finished solution, when proportioned at 1:50.
Make sense?
I looked at those formulas above. The NPK looks pretty good but notice there's no calcium or magnesium in the Grow More stuff. That's probably for incompatibility reasons with respects to phosphate. You may have close to enough Ca in the tap already for most crops, I'm not too sure for Mg
You may have to supply these separately in space and/or time in conjunction with phosphate fertilizers or phosphoric acid - I'm tying threads into knots.
Here's a useful link for fertiigation
IBT - Three Reasons to Broaden Your Fertigation Knowledge
Here's another good brand of fertilizer. Check out their CalMag Special for possible supplemental use.
http://www.plantmarvel.com
Matt