Its definitely fungus- and I agree with all of hte other commenters, you are definitely overfeeding.
It may be a resonable amount that a healthy fish WOULD eat, but your fish aren't eating it, either way it doesn't matter, you are overfeeding - a lot. To oversimplify- Uneaten food kills fish.
Adding more food is not the solution, it is actually doing more harm. Healthy fish will voraciously go after food. If they do not aggressively go after the food, it is becasue they are sick or your water quality is bad- adding more food is not the solution. Its not your food type, a healthy fish may spit out a new food type for the first day or two while they get used to it, but they will still go after it.
Its very possible that overfeeding is resulting in poor water quality, making your fish feel sick, which is causing them not to eat. It seems like you are in a viscous cycle, fish won't eat, so you add more food, which makes water quality worse, fish feel worse, eat less, you feed more, etc etc.
Do not feed more than once a day and you should never feed more than they eat.. Please test your ammonia and nitrates. If you have food growing fungus, fish not eating, new tank, all of these are classic signs of a cycling tank with ammonia problems.
I am not sure if you ever had Neon Tetra as the only fish in the tank but here is the deal.
They refused to go to the surface to eat the food the way most fish do. They refuse to go to the gravel and eat the food the way some fish and bottom feeders do.
They will only eat the food which falls in front of them in the MIDDLE of the tank.
If I place food in the tank and make it sink, there is maybe 5-8 second window in which the food is falling to the bottom of the tank.
I have a 55 gallon long take which has a lot of hiding places and rocks, plants. So the neon may not even see the food during that time period.
If I place food into the tank and don't make it sink, they will not eat any food during the first 3 minutes because its still floating on the surface. The food takes forever to eventually sink. Sometimes I leave it over night and come back in the morning and the food is still on the surface. I don't have a power filter so maybe that is why.
I am not sure if Beta mix with red cherry shrimp but maybe the solution would be to get a fish that can grab the food at the surface and make it fall for the other neon tetras fish.