As they mention, it is for mild cases. Stronger cases will require prescription meds. I've seen similar information on other turt sites, and this is pretty consistent though could use some updating. (The link for the tank... Yikes!)
Anyway, since most RES keepers are first time turtle owners (I'm only had mine for just over 3 years), I don't recommend them apply any sort of medical care themselves. This is why I don't normally suggest any home treatments - only professional care.