Might have been the extra ammonia from the food which induce the sprouting effect, but still not sure what it is.
Looks kinda cool.
Are you familiar with the nitrification cycle?
Basically it works with an established beneficial bacteria cololy processing ammonia, changing it through the process and ending with water which is safe for your tank inhabitants.
Anyway, if you have a test kit then test the water and see where the numbers fall and if they are in or out of the safe zone.
Take the sample of water to test before changing water again.
Then do a couple more water changes if you do not have a test kit / or if the water is in unsafe levels.
You can take a sample to a fish store for testing.
Generally the ragged fins could be from the water quality or time at the fish store /being shipped.
Ideally keeping the water quality in tip top condition will help with the fish's body being able to focus it's energy on healing.
Unstable and toxic water quality can harm the fish internally (sometimes you don't know about it) and externally.