I use the grow big in my hydro setup and I don't think it matters with them tbh. Back of my bottle says 2-3 tsp per gallon of water. If I were using soil I'd just clean out a gallon milk jug(s), add 3 tsp to each and fill with distilled/RO water.
Then water normally or whatever the bottle recommends. It's all the same shit as far as I know.