Aquariums: honey gourami death

any theory’s on what happened with my male honey gourami ? this morning around 10 am i noticed he suddenly was laying on the bottom of the tank on his side and swimming erratically, but couldn’t stay boyant, i moved him to a breeder box and throughly examined him for signs of aggression because he is housed with another female honey and a female betta and as peaceful of behavior as they have shown with eachother i still am cautious they could change their mind about that, im just not thinking that is the case since there was not a single nip or bite on him in sight he looked perfectly healthy and had been acting normal the night before no signs of being bullied or stressed, around 5 or so hours after noticing him and moving him to a breeder box he passed, i used a flashlight to see thru his body at his organs because my assumption is that it was something internal but everything looked normal i didn’t see any signs of parasites or internal damage as far as i could tell but idk, he was a pretty young fish i got him as a juvenile from my lfs 3 months ago, my water quality is pristine no ammonia or toxic nitrite/nitrate levels, ph sits low 7 temp 77.6° and premameters have all been stable he’s in a heavy planted 20 gal long with a sponger filter+ hob filter i’ll provide a photo of the tank