First comment is, don't dump stuff (chemicals, medications...) in the tank until you know exactly what is in there, and even then only if it is absolutely necessary.
It is more probable that what you have is harmless, as several members have already mentioned. There is (or should be) a large variety of microscopic and some not-so-microscopic life in a healthy aquarium. I have fish regularly spawning in most of my tanks, and periodically fry will survive, several sometimes. As they are unseen (by me) and are very tiny, they need minute zooplankton as food, and they find it in the aquarium. When half a dozen 1/4 inch tetra fry suddenly appear around a chunk of wood, I know they have been eating something, and it wasn't fish food that I added.
There is a complex inter-connected web of life ongoing in an aquarium. Don't disrupt it with chemicals and antibiotics, you can do much more harm than good. If something in the tank turns out to be a danger to the fish, that's different. But find out exactly what it is first, don't jump to conclusions.
Second issue I want to comment on, is snails. I cannot fathom why an aquarist would be worried about snails. They too are a part of natural life, and healthy life. They do a lot of work for the aquarist. They will not become a problem (assuming they are the common small snails like pond snails, bladder snails, Malaysian livebearer) unless something is wrong in the aquarium--too much food, dead fish, etc. So think of them as helpers, not a hindrance. I have hundreds (i couldn't begin to count them
) of Malaysian snails in my tanks, and I love it. Nothing burrows through the substrate like they do, keeping it clean and fresh for the bacteria and plant roots, a cleaning method I could never manage with all the paraphernalia we can buy.
However, if you want to reduce them, use sensible methods like removing the egg masses (pond and bladder snails lay gelatinous masses of eggs on plant leaves and the aquarium glass that are easy to see and remove), using bait like zucchini or a lettuce leaf at night, etc.
Don't ever use snail eradicators as these chemicals will affect the tank in other ways and will affect fish even if not noticeably.