Sounds like a Diatom bloom. This is normal in a newer saltwater tank. If your tank water perameters are good I would get some astrea snails. Don't worry about them reproducing heavily. That happens only with some fresh water snails.
First off , Yes you can use a nano tank and make a very nice reef tank. The biggest problem with nano tanks is maintaining water quality and perameters. Especially salinity as the lower the volume the quicker that salinity changes from evaporation. I would suggest going alittle bigger to a 24...
It should grow back in time. Also from the picture he is showing signs of stress. So keep an eye on it and watch for signs of problems. Such as ich, fungus and bacterial infections and so on. The yellow tangs tend to be less susceptable to diseases than other tangs. Good luck I have always...
Just a few of the books I would suggest are
Natural Reef Aquariums by Tullock
The Complete book of Marine Aquarium by Vincent Hargreaves
Aquarium Corals by Eric Borneman
Invertebrates by Julian Sprung
Coral Reef fishes by Peter Sales
They will get you started
I completely agree with what FSN77 said above, and would like to add that you should learn everything that you can about the animals that you want to keep. Read books, read everything on web sites such as this and ask questions. Knowledge and the ability to do proper husbandry are some of the...
I agree with FSN77. In the wild they would create a heirarchy. but in our small water worlds the third may get to stressed and die from the harrassment. Your best bet is to put the third in a seperate tank if possible or get it a new home.
if you have to have a coral out of water for a little while, with the exception of sponges and deep water corals you can cover them with a cloth wet with water from your tank to keep them. i have had to do this when fragging larger corals to smaller ones.
Although I am generally under the belief that you can never have too much flow. I think that you are going to have trouble with a tank that small trying to introduce corals without them being in a linear flow. Lps and softies will not do very well in there. IMO.
You are correct that there are very few nutrifying bacteria in the water itself. There are alot of factors involved , such as tank size, uv size flow rates. If to large of a sterilizer is used damage can occur .If to small of one or one with the wrong flow rate is used, it may then do very...
The pro would be control of paracites and bacterias in the tank.
The con would be that it does not differentiate between good and bad, and can effect the good bacterias that break down the nutrients in the tank.