Praziquantel is a medication for FLUKES, also known as “trematodes” which are microscopic parasites, and which are very common. They are responsible for transmission of MOST ulcer-disease in Koi. At least, in ornamental Koi. They have sharp “haptens” for holdfasts on the fishes’ skin and where those “haptens” enter the skin, infections with Aeromonas, and Pseudomonas can get a foothold.
Right now I find PraziPro to be the best. It offers good economy and it works well.
I think the BIG key is realizing that in colder water, the life cycle of Flukes is longer. Also, there are egg-laying and livebearing species of Flukes.
So people treat once and think they’re done. But it might be a good idea to follow label instructions or treat several times 3 to 5 days apart. In a smaller, Community Tropicals biotope / tank it’s not that bad costwise.
You should also be aware that for Flukes, it might be more economical to use Formalin and Malachite Green to clear them in very large facilities where Praziquantel might be quite costly.
You can find PraziPro online at Amazon.com, here’s the link.