honestly, i dont think that this is anchor worm. generally, anchor worm is much larger than what your describing: (
anchor worm link ) and on the end of each anchor worm is a very well defined fork (or vee). if you dont see this telltale fork on their tails, im thinking that its definitely flukes. most probably skin flukes (egglayers). i suppose that there are strains of flukes that are very visible. however, the majority are less than 1mm long.
because youve had great success with the salt dip so far, i think the dips and a bucket to bucket treatment can rid these things from your fish for good. youll have to give every fish in your tank a series of salt dips for up to three days in a row, break for 2/3 days, then a few more days of dips, etc, etc. all the while, transferring the fish from fresh clean bucket of water to fresh clean bucket of water (daily). doing this for up to 3-4 weeks could very concievably rid them all. remember, persistance is key when treating these "fish fleas".
if you dont want to get quite that intensive (and you can afford it), you could always try praziquantel (along with a salt dip before each addition of prazi). prazi is non-toxic to humans and animals and will not harm your bio-filter. however, i would dismiss the recommendations on the bottle and dose the tank every 3-4 days for up to 3-4 weeks. youll need to do a 25-50% water change/gravel vac before each fresh addition. a ten gram bottle should get you through a month pretty easily. for more on that, read this:
flukes treatments in the long run, if you find that this particular strain of flukes (if it is indeed flukes) is very persistant, there are other ways to go about it. its just that prazi and salt dips will not harm your bio-filter .
post back and let us know what you think.
paul