Just lost a very long reply which vanished from my keyboard!!
Here's the short version.
Prazi (ingredient of Mediworm) won't treat pinworms which are nematodes;
"That's what prazi is for, round worms, hook worms, pin worms, ring worms, etc."These are all nematodes. Prazi is only effective for cestodes and trematodes ( tapeworms and flukes).
For pinworms, either Levamisol or Piperazine are suitable treatments.
Although the Jungle food contains
some Levamisol, its main ingredient is Metro which is an antibiotic which works for Hexamita but is a very heavy-duty treatment to use as a prophylactic.
You can get a Piperazine Dewormer food here
http://rockymountaindiscus.com/Food_and_medications.htmscroll down for 'Dewormer'. Both Piperazine and Levamisol treat by paralyzing.
Flubendazole and Fenbendazole (variations of same drug group) are also effective wormers but sometimes hard to dose accurately and can be detrimental for goldfish under such circumstances. These drugs are especially good for Camallanus and Capillaria and are starvers (prevent nutritional uptake in the parasite)
Summary:
Nematodes or Roundworms: Best treated with Fenbendazole, Piperazine, or Levimasole.
(most common are camillanus and capillaria - Camillanus can often be seen hanging out of the fish's anus.)
Cestodes (Tapeworms) Best treated with praziquantel food.
Monogenean trematodes (flukes) : Best treated with water borne Praziquantel.
Flagellates, (Hexamita or Sprironucleus) In intestinal tract. Best treated with metronidazole.
Is it just the lack of growth that has you worried or are there other symptoms? White, slimey castings, for instance? Have you treated with Prazi at all, yet? Flukes can also slow growth.