So you have 11 fish in a 190 litre without a sump. You are pushing it there on stocking. Particularly the yellow tang which will outgrow the tank quite quickly.
Just for comparison I have a 39 gallon with 13 gallon sump, therefore extra surface area which is important for stocking density.
I have, added in this order
2 percs
1 YWG
1 Filamented Flasher
1 Bangaii Cardinal
1 Blenny
1 Royal Gramma
1 Mandarin
will be adding 1 more Mandarin (am upgrading to 6 ft) and 1 dwarf angel. Giving 10 fish in a larger volume of water and larger surface area. To be honest, the second mandarin I think is pushing my stocking but will be transferred to 6 ft before the year is out and probably sooner.
You also added your fish in the wrong order, the dwarf angel should have been last but 1 and the tang should be last the Royal Gramma should have gone in after the firefish and before the angel. You have a problem now.
I would try to catch the royal gramma and give it some time out, a QT tank is ideal for this as would be a sump. Then your firefish can settle before re-adding the royal gramma back to the tank.
Did your LFS not ask you what you already had in the tank before getting the firefish.
I would also consider dropping your fish list by 2 fish, or upgrading. You perhaps could fit more than 9 in, but you would need to monitor the levels in the tank over months to ensure that water quality is remaining good.