I am very sorry about Vampire
Do NOT mix this med with anything else. Internal parasites in goldfish are not very common (unlike other species of fish) but white waste is generally indicative of improper diet combined with stress. The white is actually intestinal cells and mucous being shed. However, there may a bacterial component to this due to your pictured fish's symptoms and some of the symptoms you mention in your fish.
I am guessing you are from European country? Your access to fish meds is very limited unless you have an aquatic vet that can help. The fish pictured had a very serious bacterial infection that needed to be addressed with pristine water and serious antibiotics. We do not know if it was the result of water quality issues, adding unquaratined fish or other factors. You did a large water change upon finding your fish unwell, so we do not know what the conditions were prior to the water change.
So, lets start with the present water parameters, any chemicals being used (ie, ph adjusters, salt, algae stuff, etc), normal water change schedule (%/#wk) and diet? Also, when was the last time you added a new fish that was not quarantined for a couple of weeks? Need to start with basics before we can figure out what is happening here.
Can you also post a pic of the fish you describe as having 'fin rot around the mouth'? This indicates very serious bacterial issues that need to be addressed promptly with antibiotics. Thanks