Dwarf gourami color change and stringy

[Smallfishvt]

Hey there! When doing my water change this past weekend in my quarantine tank I suddenly noticed a change in my dwarf gourami color that I didnt notice before. He has been in quarantine only because he was new 8 weeks ago. Would have been moved but having an issue in my other tank with neon tetras.

Tank size: 10ga
pH: 6.8
ammonia: 0
nitrite: 0
nitrate: 20
Total hardiness: 75
Total alkalinity: 0
tank temp: 75

Color on one side looks normal intensity and correct tone. Color on his other side is blackish on his head area and extreme intense blue near the gills that I dont remember seeing. Tonight he had very long stringy poo.

Volume and Frequency of water changes: 2-3x a month

Tank inhabitants: 1x dwarf gourami, 3x harlequin raspbora

 

[Smallfishvt]

Here are pictures, 1st showing poo, 2nd showing tone of left vs right, 3rd his left (the dark side with new intense color near gills)

 

[Smallfishvt]

Final picture, wouldnt let me post in othe reply this is his "normal" side

 

[Smallfishvt]

Still not sure what the deal with color was he was so good looking... But anyways he has dropsy now really bad and pretty fast. Going to have to put him down tonight so I can burry him while ground is soft before big ice/snow storm overnight