"Grams / Hour" measures how much chlorine salt chlorinators produce, BUT expressed as equivalent grams of ordinary dry chlorine.

A 25 gm/Hr salt chlorinator doesn't produce "25 gm/Hr", BUT you would need 25 grams of dry chlorine to achieve the same result.

Most Salt Chlorinators have an output control.

If your pool could be get buy with a 17 gm/Hr salt chlorinator (running at 100%), it is smarter to get a 25 gm/Hr unit and run it at ONLY 75% output. This can add years the electrode's life span.