Soil is a buffering agent and you should include that knowledge since their are soil growers and hydro growers and lots of hydro growers give advice to soil growers when you shouldn't, how are they supposed to know you are talking about growing in hydro specifically?Apparently you can....but not recommended.
The main difference that you should take note of is that pH down made purposely for hydroponics not only brings that pH down, but contains the acid's conjugate base in equal proportions which allows the pH down to have a buffering effect. Buffering effect means that when the pH reaches a certain number, the acid and base in the solution constantly react together to keep the pH steady, which is what plants need to be healthy.
Using sodium bisulfate has no buffering capabilities, so when it drops the pH, no further reactions will take place and the pH will not remain steady....which is detrimental to healthy plant life.
Here's what I found from Wikipedia.....hope this helps some.
"Phosphoric acid is also used in hydroponics pH solutions to lower the pH of nutrient solutions. While other types of acids can be used, phosphorus is a nutrient used by plants, especially during flowering, making phosphoric acid particularly desirable. General Hydroponics pH Down liquid solution contains phosphoric acid in addition to citric acid and ammonium bisulfate with buffers to maintain a stable pH in the nutrient reservoir."
Soil is a buffering agent and you should include that knowledge since their are soil growers and hydro growers and lots of hydro growers give advice to soil growers when you shouldn't, how are they supposed to know you are talking about growing in hydro specifically?