When I regularly mixed up a batches of sodium or calcium thio, I'd put 500 grams of dry sodium thiosulfate into a gal of DI water, put the jug on the stirrer, and let if stir until dissolved. After done, I'd divide into 1 liter bottles for easy of pouring.
Then 2 drops of the mixture per gallon of new tank water, per each ppm of chlorine detected, or after a time and experience, a bloop in my 150 gal tank during a water change.
To experiment and find the right bloop per water change, I either used a pool type test strip, or if in the lab, a DPD analyzer until a norm dose per water change was obvious.