I agree with Tinfoil barbs, adults though. I have some albino tinfoil barbs and I love them.
Yes, I have had the giant danios disapear one by one every night thing before. I solved it by keeping a night-light on the tank. danios(and barbs) go into a deeper sleep than cichlids do. With a night-light on very close to the tank, every one still had rest time but the dither fish could see the cichlids coming for them even in their stupor and were able to evade night attacks. Try it, it works.