mzaltadena said:I have owned many betta before and have kept them in small containers and they do just fine, and last a long time.
That makes me sad. "Last" is entirely the right word. If given a properly heated and filtered tank, these fish "thrive". Human beings can "last" many years in a jail cell. I wouldn't call that a proper life.
Both of the fish store employees you spoke with gave you iffy information. Mollies and African cichlids (unless a shell dweller as someone else pointed out) as well as goldfish are not appropriate for a 10 gallon tank. Neons can be sensitive fish and I would not recommend them to cycle a tank. Saltwater is more expensive to set-up than freshwater, and requires a great deal more work when it comes to setting up your water parameters.
Since you have decided to do a fish-in cycle, you have some work cut out for you. You should be testing ammonia and nitrite daily, and in some cases, more than once a day (morning and evening would work). The water needs to be changed immediately if either spikes to minimize harm to the fish. Keep in mind that once bacteria have established and the cycle completed, you have only built up enough bacteria to support the single fish you have in the tank. Any time you add new fish, the tank will cycle all over again as the bacteria builds up to support them. Fish-in cycling is a lot of daily testing and water changing over a period of months until you get your final stocking.