Hi Gianne,
This is really sad and I can very well understand why you are depressed. But I think all of us must earlier or later learn how different paros are from what we are actually used to when it comes to any kind of special treatment/feeding or whatever.
I personally don’t know what was in your medication that made them die but maybe there are some other people who have any ideas.
In general, I think your deworming day is of no good for the paros. First of all, I would not really consider blackworms an appropriate food for paros especially if they are from a local shop. These life foods are usually in no good conditions which makes them vauable in means of nutrients for the fish. They can actually starve to death because they dont get enouch nutriens out of these worms. Something similar seems to be known from too old and non enriched Brine shrimp larvae.
Besides this, if you provide the necessarily low ph and the water clean, there will be almost no germs certainly including these special worms you fear.
It is a part of the message of the paroproject that for actual aquaristics, almost none of the medications, chamicals etc. that we like so much to throw in our tanks are needed, some are even leading to fatal events.
Personally, I am convinced that neither of our fish need external chemistry-support unless they show real signs of uneasieness and are visibly suffering. This is of course a question of observation and feeling in your belly what your animals need. No fish that is kept with appropriate kind and amount of food and in fresh water with the needed ph, EC etc. is in need if such things since if else, they would not survive in nature.
My advise would be:
Keep everything running as before since they have apparently liked it very much. Stop feeding bought livefoods and blackworms. In the summer, The best imaginable food source are black mosquito larvae which you can easily grow in almost any backyard in a pot of water and hay. In winter, mine usually live on microworms and Brine shrimp naupliae…
Greetings Rafael