I have a 10 gallon tank intended to hold 6 danios. we started the tank with three regular zebra danios And once it was cycled intended to add neon danios. However I keep having the neon danios die on me. all three original zebra danios are doing swimmingly. they are in perfect health, they eat well they interact well with no significant aggression and seem to be doing very well. my neon danios are not doing well. most often they do not survive more than a day or two after being introduced to the tank. meanwhile the normal zebra danios continue to do fine. I have lost count of how many dead neon danios I have returned to the store. Is there something I'm doing wrong or are neon / GloFish danios just more fragile? should I give up?