Just noticed today that my 1 male Dwarf Gourami is acting and looking strange.

Its hardly swimming, just sitting on the bottom and it's head has lost its blue. It's almost a dirty grey/brown colour.

The water is fine including temperature. In the past week though I have changed a lot in the tank, planting live plants etc.

Just today I've put in 4 red honey dwarf gourami. LFS said they would be compatible and he gave me 1 male, 3 female of them. Dunno how he could tell difference I can't lol.

What's wrong with him? I don't want to lose him.

Was he OK before you added the Honeys? How long have you had him? He may not like the newcomers as DG are territorial fish and though they aren't the same species as him they are sufficiently closely related for him to feel threatened by them.

With the Honey Gourami you can usually tell the sex even when they aren't showing breeding colours in mature fish by the shape of the dorsal fin. In males the end of the fin is pointed and in females it's rounded. However, in juvenile there's very little difference