The usual way to clean fungus off lenses is to use a 50:50 solution of ammonia and hydrogen peroxide and a cotton bud. I assume that people mean supermarket ammonia (2%) and supermarket/pharmacy peroxide (3%)
Pure peroxide is rocket fuel, wheeee!
I used this mix today on an old multicoated Pentax lens and it is definitely coating safe.
Apparently concentrated fungus comes off like butter with this solution. I did it as a bit of a precautionary measure because I couldn't tell whether it was fungus or not. Hydrogen peroxide kills fungus and bacteria, you can use it on yourself too.
If you do use UV, make sure you use a germicidal UV tube, not just a blacklight. And stay the heck away from it.