woot, sorry didn't realize it at the time but you had already said in the title that it was a firebelly...
do you happen to know more precisely what kind? Japanese firebellies are hardier than Chinese ones, for example, and so-called warty newts (Paramesotriton) are sometimes sold as "firebellies" and require somewhat different conditions (i.e. a slight current) -- post a digital pic if you can
it is OK to have a not-too-powerful internal filter running as long as the tank is large enough and the water is not swirling around -- Cynops species are generally pond/paddy dwellers, not river dwellers
-- you can have the filter output run out over a rock or something, or block it with artificial plants -- as long as there is no significant current like Jen said
check out her setup (No. 3) at this page:
http://www.caudata.org/caudatecentral/tanks/setups.html
how long did you leave the worms in the water? if the water is cool (and it should be now if you're living in the Northern Hemisphere and not Oceania), then you can leave them there for several hours without worrying about them decomposing
if your newt or newts are not too skinny already, you needn't panic about them not eating right away as they can go for quite a while without food...though they should begin eating soon if all is well
keep them in at least several inches of water like you're doing now, not just half-covering their body -- but give them something to climb up on for when they wish to temporarily leave the water (like an artificial floating island sold for turtles)
put some plants in the water too to help them feel at home and to break the monotony of a bare tank
make sure the lid is secure as they can climb!
have you got one newt there or more than one?
good luck!}
