I just made this the other night. Its pretty cool. Figures out all the numbers for you. If you want to add a certain ppm to a certain growth stage, just type in the ppm at the growth stage your at and put in how many gallons your res is, and there you go. I added Cal-Mag to this too.
Here's the calc with no info in it.
I inputted 900 into the Veg stage and it tells me ow many ml per gallon.
After that I inputted my res size and it then tells me how many ml, tablespoons or teaspoons to add in total.
Pretty cool, I think......