what is wrong with my fish?

[siang]

i have a community tank, its nearly 4 months old. water param's are fine. i have 2 red honey gourami. one is perfectly fine, the other is listing to one side and staying at the bottom of the tank. he looks normal, and doesnt seem distressed, just very lethargic. any idea what could be wrong? i had one of them die a couple of weeks ago, got up in the morning and he was dead n the bottom of the tank. so far ihave had 3 gourami die in my tank, the red honey, and about 5 weeks ago, 2 blue dwarf gourami. no idea whats going on with them