Your tank really looks good.
I agree with blue the damsels are terrors. I have one in a tank as an only fish but I have seen him pick up a snail and just swim away with it and drop it somewhere, it tries to do that with the hermit crab and emerald crab as well. You might want to check out this on cardinal fish http://www.liveaquaria.com/product/p...6+85&pcatid=85
. I believe they are nocturnal.
Diatom algae is normal in new tanks, do some water changes, cutting back on feeding and lights will help but usually it burns itself out.