Yes that is what it means. Values were for 5 gallons.
So 40ml=160ml. for 20 gallons.

A note about Calmag+ and hardwater GH MicroH.

If you end up with GH 3-part, part =MicroH, the difference between regular GH Micro, is that Hardwater formula has less Calcium-magnesium in the formula. so don't forget you calmag+...Your plants use alot of these 2 elements.