The most commonly used concentration is 0.2g/l.
In regard to water versus chemical cleaning it is an area of contention.
You can remove the ribo, wet or dry, with water only. However, when the ribo is allowed to dry the amount of water needed to remove it is far greater.
In a Factory Acceptance Test (FAT) at a vessel fabrication facility they generally only have water available and would prefer to do a wet ribo test. The end-user generally wants to see dried ribo because this is seen as more thorough.