1% = 10,000ppm
So 1g/iL would give you 0.1% or 1,000ppm
0.5g/1L would give 0.05% or 500ppm, etc.
GAA is not super soluble. The best was to dissolve is by adding enough 1N sodium hydroxide solution (caution corrosive!) to dissolve the GAA, this should only be a few ml at most. Then top the rest up with water.