How do you define "internal parasites"? Popeye is highly indicative of an internal bacterial infection. White poop, however, tells you nothing, really. Your fish could have been starved, the bacterial infection may have altered the function of the gut, could have been virus - or, as you suspect, it may have been an internal parasite. All kinds of things can cause white poop - you shouldn't assume it's a parasite without further information. By parasite I'm referring to a worm, protozoan or other "large" pathogen which is neither a bacteria or virus. You have to be careful with your terminology as this will affect how people assess and help with particular problems. This is turn will have a big impact on choice of treatment and make the difference between saving a fish or watching it perish. For example, Maracyn-II could be used to treat a bacterial infection, but would not be effective against an internal parasite. Similarly, many medications that are effective against internal parasites (which can be very difficult to select since you need to know what type of parasite you are dealing with) would not be effective against a bacterial infection.
Better luck with your next set of clowns.
