Newbie

[figdish]

Hi all, I am new to saltwater tho have been running freshwater of all types for years. I have googled, been to every fishstore in town and have been givin all sorts of info. I have a 30 gal that was already established when I received, have added a few fish and some live rock. I was told that a back filter is sufficient for this size of tank but my water looks slightly cloudy even after 25% changes.
What is a nano, what is a sump pump and what do I need?
If anyone can advise what type of filters, sumps or whatever it is I need I would be greatly appreciative.
Also I have some algae/fungus that I am not sure if nuisance or to leave it.
How long does it take before you start seeing growth on live rock. Can I introduce plants? What fish will not eat what plants? How many fish in saltwater is too much for 30 gal?
So many questions, so little time.
thanks again for any/all advise
figdish