Assuming SIN and room with open windows. RH is 60% above. So from the start, either your silica gel is already exhausted or the hygrometer is faulty.
As long as there isn't not a big hole in the box, a typical 500gram of fresh silica gel can get a 20L non airtight toyogo box down to 40-43% in 4 days.
You did not explain how big the box is and what is the color of the silica gel now. You cannot expect one tablespoon full of silica gel to dry the entire 20L box. So if the box allow, use the full 500gm but never every allow the equipment to come into direct contact with the silica. Even a piece of card in-between will do fine.
The common sold silica gel from camera/film developer shops are blue indicator -> pink (dry, wet). While the less common is the orange indicator.