I haven't had to add any salt to the tanks yet, have fairly hard water here that seems to have lots of salts in it. My axies only had afew each that i pulled off when they were alive and less fragile (tell you the truth i wasn't sure what they were until i pulled them off and looked under a microscope and searched the internet) They are quite gross up close, spewing eggs/larva/nauplii everywhere. I took the carbon out of the filter like the box says and put one tablet into a 10 gallon tank (half dose) That was weeks ago and i haven't seen any come back yet. The box recommends three treatments a week apart (for fish) if i remember. My friend had anchors at the same time and tried the API treatment and it did not work at all, hers are back with a vengence. Pretty sure the anchor worms came from the pet store as we both got them from same place. That leads me to believe the Parasite guard works as I seem to have gotten rid of them. And it's so cheap i am going to quarantine feeder fish from now on and treat them with it so i never have them again, or just stay away from feeders.
Another thing i did at the same time was crack a window in the basement and lowered the temperature to 12-14C for a few week as my search of the internet found a paper that said that anchor worm cycle cannot continue if temperature is less than 15C. Not sure if true but since axies like the cold i tried it too. I guess fridging axies would do this as well if its true.
Anyways sorry to get long winded, search this site and the internet about the ingredients of Parasite guard, from what i remember they were all either safe(ish) or not on any DO NOT USE lists that i could find, and then decide if you want to use it. I checked on my guys twice daily at least with a flashlight loooking over every inch of their body checking for worms and any signs of stress (if stressed would have pulled them out of tank, but they never showed any signs of stress with this treatment and ate like the pigs they are the whole time).
Hope that helps,
Good luck,
let me know how you make out and what worked for you in case i have to deal with these nasties again.