I am using 5 zebra Danios to cycle my new 70litre tank. I got them today and of course, ammonia levels are at zero. One of the zebras is looking pretty poorly. He is very pale and barely has any stripes visable. He is the largest and most active yet he doesn't look well at all. He does have white spots on this under side but it doesn't look like white spot just his natural colouring. He keeps bullying the others slightly and can't seem to relax. Any ideas?