Hi Bill,
I think treating them for worms is the way to go here, but on that vermisol... I haven't tried feeding it...I don't think there would be an issue with the carrier in it...still I just can't say for sure..
I would dose the tank water initially since you know its safe... then scope the feces after a day or two and see if theres worm eggs still.. If there aren't that would give us alot of info and if there are...well that says alot too.
Conversely, since they are eating, you could feed them a panacur(fenbenazole) based food... There are many commercial sources for flakes medicated with this at the proper concentration.
hth,
al