You would get some beneficial bacteria from the water see if you can get some 200 micron filter socks as this will catch some of the nasties that you would not want in your tank. I would ask them if they have had any fish show signs of ICK or any other sickness as they could have very healthy fish that can fight off ICK. But it can still be present in the tank water and seems you have fish in yours it would give the parasites a place to grow and reproduce. You could have done a cycle with a raw shrimp tail, all the biological bacteria need is something to feed on and grow as your system starts to mature. You have read some stuff but a tank can take several months to mature to a point where you can put just about any fish in it. Some fish need a very stable and establish system or they will not make it. just like a Nem you should not put one in a tank until the tank is fully established. There are a few Nems that will survive and thrive when in a tank that is not very good but it is still not a good idea to put one in.Some fish need certain conditions to survive long term and that is what we are all looking for. Too recreate the oceans reefs be it a passive, tang , or predator tank. Just make sure that you provide and establish the right things for the fish you want to keep before you add the fish.

Bill