100 teaspoons is just over 2 cups. Unfortunately weight and volume can't be compared withough't knowing the exact specific density. Typically 2 cups of dry
nutrient would weigh at least 1 lb. If 2 cups of the RAW
nutrients only weigh 2 oz, it's extremely light in weight for a dry nutrient. But teaspoons and milliliters are both measurements of volume and can be directly compared.
1 teaspoon= 5ml
100 teaspoons= 500ml
There is 237ml per cup.
2 cups= 474ml
I'm trying to calculate how economical those nutrients are, and if I go by what you originally stated, you paid $90 and say it will make about 400 gallons of nutrient solution. Going by that, $90 divided by 400 gallons= $0.225 (about 23) cents per gallon of nutrient solution.
However from your second statement, it sounds like your taking all 7, 2oz containers and mix them together making 14 oz. total. But from what I read from their chart and directions, it doesn't work that way. You should be using either Gro or Bloom (or like I mentioned they will probably tell you for continuously fruiting plants 50/50 of each) at a time. And their directions say 1-2 teaspoons per gallon of water. All the other parts are additives that you add in addition to that, in the same 1 gallon of water. So even though you have a total of 14 oz. of products you only have 4 oz. total of the nutrients (Gro and Bloom).
Since I cant compare weight to volume, I can only go by you saying that 2 oz= 100 teaspoons. So in reality you have 100 teaspoons of Gro, and 100 teaspoons of bloom for a total of 200 total teaspoons (gallons of nutrient solution) maximum. So using these figures
Using only 1 tsp per gallon (50% strength)
$90 divided by 200 gallons= $0.45 cents per gallon of nutrient solution.
Using 2 tsp per gallon (100% strength)
$90 divided by 100 gallons= $0.90 cents per gallon of nutrient solution.
To be considered cost effective, I have a threshold of $0.15 cents per gallon (maximum) cost per gallon of nutrient solution to consider it cost effective. That's $0.15 cents maximum, but I prefer it to be under $0.10 cents. But can even get that below $0.05 cents per gallon when buying quantity's.
Part of the reason I wanted to know why the additives are added/needed is to break down the cost effectiveness. But also to find out if their needed at all because they shouldn't be if your using a balanced stand alone nutrient which they claim the Gro and Bloom formulas are. Not only would eliminating unnecessary additives significantly reduce your cost, but adding mineral salts to an already balanced nutrient will knock it out of balance. You don't just want to be throwing stuff in because the package looks good, you can easily throw off the chemistry. You can even wind up with some elements reaching toxic levels. If your adding them, you should know why your adding them.
Cost effectiveness aside, before I could give an opinion on your nutrient solution concentrations, I would need to know what your putting in it and why. As well as in what ratios compared to the recommended concentration's and water volume. So far I don't have any answers to why all the additives are being added, nor do I know what specific amounts your adding per gallon of water. Then I can get into things like how big the plants are, how many your growing, and total water volume in the system.