Strange formation on Hoplosternum thoracatum belly
My beautiful Hoplosternum thoracatum has a strange white formation on its belly. He has it for a very long time (counting a couple of months) and it neither increases nor decreases, it looks like the formation of his own body and not some kind of external object (I may be wrong!). The fish feels well, eats very well, is very curious, cheeky and his behavior has not changed in any way that would indicate any problems. But that thing on his belly worries me very much. What it is, it is dangerous to him and other fish?
The tank is 200L.
All parameters are good. I change about 30% of the water once a week. I feed my fish twice a day, mostly they eat frozen food bought in a specialized aqua store. I use plant fertilizers daily. No angry or aggressive fish, lots of plants and places to hide.
He started to lay on the surfaces in a strange position. His head is on the ground, bus the back part is raised up approximately 45-50 angle. Is it normal? Please, help me, I'm really worried about him and don't know what actions I should take if any. And that thing on his belly is still present.
In the "dark" photo he is in his laying position with up back part and you can see better that thing on his belly as well.