nematodes, formalin

I had posted a few months ago with the goggle-eyed dollar sunfish. I was advised it was nematodes, and sure enough, I was able to actually see the coils of the nematodes through the tissue around the eye. I have also had problems with bantam sunfish (in the same tank) bein g covered in white slime. Despite this, the bantams continued to feed and act normally. That is, until they died. I had the impression that nematodes can also cause the body slime. All these fish were wild caught using minnow traps (i.e., small). They were maintained in a 70 gallon tank. Recently mortality has picked up and the tank is decimated. After about 10 months perhaps a dozen fish are left. The signs if illness preceded any deaths by several months. I plan to tear the tank down and begin again. I have heard that public aquaria will dip fresh-caught fish in dilute formaldehyde solution to kill any parasites. This also kills the fish sometimes.

Anyone out there have experience with the formaldehyde pre-treatment? Are there any treatments for parasites that would control these nematodes?

I don't think a formalin dip would do a lot for nematodes. Dips are good for parasites which live on or just under the skin, but nematodes are nasty critters which venture all throughout a fish's tissues. Many of them have a direct life cycle too