Most common causes and obvious present from the amount of film in tank and how else do I know. . . Been doing this 36 years and NEVER ever have this because I control my nutrients.
Diet- Omega one-bloodworms-mysis does not furnish this carnivore wh is a sand sifter enough meats, fatty acids and omegas to thrive hence its thin body. Mine gets shrimp, krill, mussel and plankton to supply its needs for meaty foods and will certainly scavenge for other foods like copepods and brine shrimp.
This fish is obviously starving why it is thin despite being fed