A standard 20g tank is not sufficient space for danios, whatever species or type. Danios are very active swimmers, and they need space. If this is a 20g long, with a length of 30 inches/75 cm, it can work, but a standard 20g high which is only 24inches/60 cm long is not enough space. Danios are shoaling/schooling fish, so a group of 10 or more is needed as well.
On the "glo" fish itself, these should not be acquired on moral grounds. This is not a natural species, it is a man-made variety and on an ethical note the hobby does not support such things, however they were achieved. The only way to stop this practice is not buying the fish. They are prohibited in the EU and the UK (if memory servs me correctly), they should be elsewhere as well.