Unfortunately, before I could try anything else, he died. Poor guy, he was a good fish. He also had long stringy poop, which I also saw is a symptom for DGD. My water conditions are good, I'm hoping it was that and I don't have any more problems with the other fish.
Thank you everyone for your advice, but if it was DGD, there was nothing that could be done. I won't get another Dwarf Gourami, though I really like them.
Wouldn't you like to beside the seaside?