There are 128 liquid ounces in one US gallon. So instead of preparing 128 gallons of solution you can prepare 1 gallon stock solutions (128 times normal strength). Then all you have to do is add one ounce of each stock solution to make one gallon of nutrient solution.
If you are using 3 liter soda bottles then you should enter 300 liters instead of 128 gallons. Instead of preparing 300 liters of solution you can prepare 3 liter stock solutions (100 times normal strength). Then you will add 10ml of each stock solution to make one liter of nutrient solution.
If you are making your own formula then you need to take into account the solubility of the various salts when preparing stock solutions. You do not want the salt to precipitate out of the stock solution (too concentrated of a solution). You should have no problem in preparing stock solutions of 128 times normal strength with commonly used salts.
Example of salts with low solubility include superphosphate and triple-superphosphate. These salts are rarely used in hydroponics.