DONT TAKE UR MONITORS NEAR ANY BEACH!!!
You shouldnt take your herps out on any public property without permission from the government that owns the property. And there are beaches all over that are not effected by this oil spill, though a huge portion of the US's ecosystems have been effected, thanks to the inability to cap a spill by BP.

Also why would this be affecting any herps that are being sold? I know alot of monitors are WC imports but the water monitors we have are from Africa. Which has not been directly effected by the spill to my knowledge.

And you may want to contact the vet and ask the specific name of the parasite. Knowing that yourself can't hurt, and may even help you in the future. Is the vet a certified herp vet? Do you know if they deal with herps on a regular basis? Unfortuneatly some vets will diagnose when they dont truly know what is going on, and may just blindly give you a prescription and doing shotgun anti-biotics can sometimes be even worse.

And as asked before, do you have details on your setup? Temps, substrate, humidity and the way you are measuring the temps/humidity. Monitors like is HOT. A 130-140 degree SURFACE temperature is what is required and sometimes keepers will have their surface temps upwards of 200 degrees. Note this is a surface temperature. If you do not have one already, buy a infra-red temp gun. This will save stress on your and more importantly help your monitor to thrive.