Hello, I breed danios last week. what I did is:
set up a 2ft tank breeding tank and set the temp to 28 degrees(normal tank temp is 25).
Breeding tank has a single layer of 15-20mm riverstones, this is so that the eggs can drop inbetween the gaps. Some poeple use marble, but there are expensive.
In the evening I put the danios(I have only 5) in the breeding tank. Next morning remove the danios. After about 5 days you will see fry sticking to the glass.
I have read info that danios are loyal partners, so I reckonmend putting all the danios of one breed in for breeding.
Be warned, the babies are small, you will need to feed infusia and rotifers for the first week and then baby brine shirmp.
infusia recipe: glass jar with tank water plus a piece of lettuce, leave in a warm place. After 3days it will be ready. Use eye dropper and put same of the cloudy water in to the tank.