It may well be the tank light that is the problem. This species does not like bright overhead light. In its habitat--it is believed to be endemic to the upper Ayeyarwaddy drainage in northern Myanmar--it is found in small streams in the hills, having a gravel substrate with small rocks and thick terrestrial vegetation along the stream banks. A stream aquascape having a dark gravel (sand is fine, especially as the cories need it) substrate, rocks, and side plants would provide an ideal environment for a group; floating plants would reduce the light, providing the shading this fish prefers. It spends time at the surface, and is an adept jumper and will find the smallest opening, so the tank must be securely covered.
Good floating plants that will get thick and provide exactly what is needed here are Water Sprite or Water Lettuce. When the tak light comes on and goes off--which should be on a timer to ensure consistency each day as this does affect this and most fish--make sure there is good ambient light in the room.
On a taxonomic note the genus holding this species is now considered to be Danio. Originally described by Hora (1928) as Danio (Brachydanio) choprae, it moved into the genus Brachydanio erected by Dr. George S. Meyers (in the early 20th century) when he divided the "Danio" into three genera, Danio, Brachydanio and Daniops. During the latter two decades of the twentieth century, many ichthyologists had doubts about the validity of Brachydanio, and in 2003 Dr. Fang Fang determined that the genus Danio was paraphyletic [Greek para = near and phyle = race], which means the genus contains its most recent common ancestor but does not contain all the descendants of that ancestor. Danio was restricted to the nine species of the Danio dangila group comprised of the smaller-sized species, and the genus name Devario was suggested for the remaining larger-sized species. The former genus Brachydanio was disbanded. Kottelat (2013) placed it in Celestichthys but this was short-lived, and the species was also considered in the genus Brachydanio by Kullander (2009, 2012, 2015, and 2016) and this is the accepted placement.
References:
Fang, Fang (2003), "Phylogenetic Analysis of the Asian Cyprinid Genus Danio (Teleostei, Cyprinidae)," Copeia (no. 4), pp. 714-728.
Fang, F., M. Noren, T.-Y. Liao, M. Källersjö and S. O. Kullander (2009), "Molecular phylogenetic interrelationships of the south Asian cyprinid genera Danio, Devario and Microrasbora (Teleostei, Cyprinidae, Danioninae)," Zoologica Scripta volume 38 (no. 3), pp. 237-156.
Kullander, Sven O. (2012), "Description of Danio flagrans, and redescription of D. choprae, two closely related species from the Ayeyarwaddy River drainage in northern Myanmar (Teleostei: Cyprinidae)," Ichthyological Exploration of Freshwaters, Volume 23 (No. 3), pp. 245-262.
