Good start Paul! We're on the right track!
Jim, your tank is still in it's young stage. Don't be to worried right now. Be sure to use only RO (preferably RO/DI) water for top-offs and when mixing water. If you haven't been, I suspect it's likely you have phosphates and nitrates that are bound up in the algae now and for that reason, not registering on your test kits. In addition to number of snails and crabs:
What kind of bio-filtration do you employ?
What kind of corals do you have in the tank? You say they are turning white, are they SPS?
What kind of lighting do you have?
Regarding the green 'sheet algae', is it growing like the purple coraline does? If that is the case, relax, that _is_ coraline, just green coraline.
As far as the
bubble algae goes, some recommend emerald (mithrax) crabs, some recommend a fish whose name escapes me.
If you are keeping sps, and it indeed is bleaching, I'll leave that to someone else.