If you are in the UK you are in luck, as I've used a UK sourced IP med, flubenol-15, successfully several times. I'm generally dubious of products you add to the water, but this stuff definately gets into the fish and kills the parasites, and has the side benefit of killing any worms segments in the water or filter, where IP foods can't. Cream colored stringy poo is almost always IP, if you go to
http://www.flubenol.co.uk, you can order a batch, it works very quickly, I saw a figure 8 that was a skeleton with some puffer skin stretched over it and pooing kite string anytime he ate start pooing Grey to brown lumpy chains the day after treatment, and he is now a total butterball, who my GF and I must slow our feeding of lest he develop health problems from overeating. I'm not associated with the makers at all, I just have direct experience that it does work as it says it does, and that it does seem every bit as safe as they say it is, and when you are sure a product saved a pet you care for when other treatments failed, you are quick to suggest others use it.
No matter how magnificent your successes or devastating your failures, the worlds' approximately 5 billion impoverished people could not possibly care less.
Some call it a product of a mis-spent youth, I call it Rock n Roll ! 
