Did you notice a little white spot on the fish, or just the worms themselves, Ich usually starts with the "White spots" first, then use Ich treatment, but if worms are already appearing, it could be internal parasites, I would still use Epsom for the first 3days, and not use the Ick treatment for now..
I noticed two white pimples on neon first and then a couple of days later my betta became ill. Upon close inspection, there appeared to be the tiniest little white worms crawling on my betta. That's when I dumped in the Super ick cure treatment. So far so good............
My plakat gets them on him when he's been hunting through the weeds in his tank. They drop off after a while, disappear.. they eat fish poo and junk at the bottom of the tank and usually aren't seen at all unless there's too much food/waste lying around and a population explosion happens, or there's a major change in the water that drives them out of the substrate. If you've recently medicated your tank, that'd do it.
Could be gill parasites, but if it was that he'd have been sick as a dog long prior to being exposed to ich medication if he's this sick and there's enough flukes, and big enough ones, to be seen crawling all over him..
Did you medicate the tetra? If so, did you do so in the tank (I'm assuming the betta is in the same tank)?..
If it was in the tank, was the betta sick like this -before- the medication? Or did you not medicate the tetra and then the betta got sick, and then you added ich cure?
These details could help figure out what's wrong with him. Please don't panic-medicate, as too much/unecessary/wrong medications can actually cause your fish to become sick...
I treated all fish with the following and never secluded any fish:
The very first thing I did was add aquarium salt to treatment levels. After I felt that had no effect, I did two days of Pimafix. Worrying that it might be ick, I did a large water change and then added Ick treatment to the entire tank.
But the part of the ich life cycle visible to the naked eye doesn't look like "worms" at all. (Not to say he doesn't have ich - in fact, I'm betting on it..)
It's just that there's no 'worms' I've found that would be crawling on the fish's skin.. whereas I've seen planaria do just that to my plakat, pretty regularly with no harm done.
I'm attempting to help the fish avoid the stress of extra medications if they aren't needed... so some more info on these 'worms' would be great.
The worms looked exactly like planaria, which is what they probably were. It's just the first time I saw them crawling on a fish. Also, a neon tetra was scratching himself on the rocks. So, most likely ick/parasite, and ick treatment should solve the problem.