Those fish in the photos are
Corydoras trilineatus. For some reason stores often (if nbot almost always) label them as "julii" but they are not. "False julii" is a common name that really should not be used [over on his site CorydorasWorld, Ian Fuller will not tolerate the name
] because the species is distinct and named/described.
This is one of four very similarly-patterned cories that are frequently confused and will often be seen in stores under incorrect names.
Corydoras julii, C. leopardus, C. punctatus and
C. trilineatus all share a large black blotch in the dorsal fin, a barred caudal fin, and a horizontal stripe along the body at the juncture of the dorsal and ventral lateral plates; the body is spotted. However, all these species are highly
variable in their patterning on individual fish.
The species
C. trilineatus usually has a reticulated head pattern and the body markings are more variable than
C. julii which always has a spotted head and body and is somewhat smaller and more compact-looking in size.
I would strongly recommend you change the substrate to sand though; this does seem to have an impact on all cories long-term.