I have a tank 1 mono 2 mollies 1 is pregnant all doing good. Any damsels died sea slug died I have 20 snails all doing good. Put in a big eyed squirrel looks bad. Than i put in a med-large lion fish and a blue spotted sting ray. Both seem to be doing good. Why would some prosper and others die? The ones that died ended up with what looks like white spot. My tank is a 75 gallon 75 pounds of live rock no portien skimmer yet as I just put in the lion and the ray (which I named Jasmine) 2 days ago my levels are perfect just wondering if there is something else.