Gourami Sick or Injured HELP

My Gourami appears to be injured badly or has some sort of infection, completely new to the forum so apologies if this is in wrong place. Is anyone able to tell me what this may be

 

This didn't happen overnight I think? Some extra info is needed.

 

This didn't happen overnight I think? Some extra info is needed.

Litrally happened over night, had the Blue Dwarf Gourami for about 4 weeks now, last night went to bed after turning lights off and he looked perfectly normal and had normal behaviour, woke up this morning and he looked like that :L He's passed away already and now I'm worried as have a Pearl Gourami that got placed into tank this morning. So I've put the Pearl into a different tank incase it's been infected with whatever it was that killed the Dwarf.

 

What tanksize, other fish, tested your water?

 

What tanksize, other fish, tested your water?

Put the new gourami into a 54Litre tank but the main tank the Dwarf was in was 180Litres, current fish in 180 is 5 Guppies, 4 betas (one male 3 female), Albino Cory, Pleccy, One Algae Shrimp and Two angel fish. Don't have a test kit as went to petshop today and they didn't have any in, Ower of shop said she would bring a test kit in from home tomorrow. Other fish are behaving normally so I'm pretty sure it's not ammomia burn or lack of oxygen.

 

With progression I'd say a bacterial issue though a DG and bettas won't be friends I'd say.

 

With progression I'd say a bacterial issue though a DG and bettas won't be friends I'd say.

Thanks for the advice, Really new to fish keeping so doing as much research as possible to give the Lil guys a good time. The male betta I have is pretty passive, Occasionally he flares at the largest female betta but they both go their separate ways afterwards. provided plenty of hiding places aswell.
One fish I forgot to mention was a male swordtail who's been in the tank longer than the DG. I've noticed him nipping the DG in the past week but the DG wouldn't flee it would just remain there and take it.