Sparkling gourami swimming "tail heavy"

[Greenlikeafox]

Hello beautiful people. Need some help. One of my sparkling gouramis is swimming funny. Slightly jerky, tail sinks down if still. How it's pictured is how its been for a day and a half now. There is tail movement so I don't think paralysis (although it does look like it at times).  I've had it maybe a month and its still a juvenile. 

Everyone else in the tank isn't showing any signs of distress, injury, illness, or aggression. Tank mates: sunset honey gourami, royal blue dwarf gourami, chocolate gourami, older sparkling gourami (rescue), 3 female lemon tetras, and 4 golden white cloud minnows. 

Tank is a 16 gallon Biorb with upgraded under gravel filtration. pH has been around 7.6 for months (and only this tank- assuming due to the biohome filtration media). (Been cycled and stable since May).  Water is on the harder side but no copper. Nitrate between 0-10, Nitrite 0, KH around 80, and no chlorine. These have been the stable numbers since cycling completed. 

Its planted with swords and anubis, larger sized white gravel,  and some water spangle. I test every week and do 20-30% water changes when necessary which is about 2 weeks.  

[Colu]

Fish sometimes do this when there weak has he been eating ok any signs of parasites White stringy poop flashing heavy breathing what food do you feed them 

Edited October 29, 2021 by Colu