Cherry Barb Died And White Mark On Gourami?

Hi all sad news i woke today to a dead cherry barb  . I checked all the water perameters and nothing has changed.
Only i have 2 new fish 1 clown pleco and 1 dwarf gourami. tonight i noticed a white patch a couple of mm on the gourami and not sure if this is an ulcer or if the problem in the tank is the new pleco?
the rummy nose that had a brilliant red to them have also went pink.  gourami still going up and down the glass. if i seen the plec doing anything then i could put him in a keep tank and rehome but when im watching he is just relaxing.

Any advice is gteatly appreciated

The rummies noses suggest something not quite right. Whenever they go pale, be alert for something in the tank.
Have you been checking your ammonia & nitrite since you added the new fish? It could be something as simple as your filter bacteria having to catch up and causing a mini-spike.

It is possible that the new fish brought in a sickness - how long is it since you got them, long enough for the other fish to catch something?

Definitely goodle dwarf gourami iridovirus and see if the symptoms of that apply to your fish. But white on a fish could also be whitespot (salt grain-like spots), fungus (actually a bacterial infection) or saprolegnia (this one is a fungus). You'll find these described in the Articles section, Health subsection.