Kuhli Loach Losing Weight Even Though It Still Eats

[emmaorabelle]

Hi everyone,
I’m a bit worried about one of my kuhli loaches and wanted to see if anyone has experienced something similar. Over the past month, one of them has gradually become much thinner than the rest of the group. The strange thing is that it still comes out for food every evening and seems interested in eating, but its body looks noticeably skinnier now, especially around the middle.
The tank is a 30-gallon community setup that has been running for over a year. Water parameters are stable: ammonia 0, nitrite 0, nitrate around 10–15 ppm, temperature 25°C. Tankmates are peaceful, and there’s plenty of cover with driftwood, plants Trees Hate You, and sand substrate. I feed sinking pellets, frozen bloodworms, and occasionally live blackworms.
I haven’t seen any bullying or obvious signs of disease, such as white spots, fungus, or redness. The loach is still active at night, but during the day, it hides more than it used to. I’m starting to wonder if this could be internal parasites or some digestive issue.
For those who’ve dealt with skinny loaches before, what ended up being the cause in your case? Did medication help, or was it more related to diet and competition for food?