Resources when facing fish health diseases, symptoms of illness like white spot, and parasite treatments.
There is a lot of information on the internet but it can come from inexperienced sources, and in many cases now, may be a 'bad-translation' of stolen content. It's a "thing" these days.
"Change enough words and it's not plagiarism!" so they say. And when non-English speakers are 'changing words' I've seen some amazing errors.
The best fish health information can be found on DrJohnson.com because it's coming from ONE person and not a panel of self proclaimed experts. (Forums)
Other sites in the same family include: Fishdoc.co.uk and Koivet.com
But, sometimes you don't want a computer near the pond, and prefer details in a written paperback format so, perhaps your best bet is Dr Erik Johnson's textbook "Koi Health & Disease" 2.
It's written in a cookbook "How to" format that almost anyone could understand. It's been well reviewed. In fact, the ONLY criticism of the book on Amazon.com is that the images inside the book are black-and-white greyscale. You don't lose any information with that, but people expect full color these days.
Another resource is Fishtreatments.com (A sister site to drjohnson.com) Things are different on that site.
At that Fishtreatments web site, which calls itself a "What To Buy For That Bug" web site, you get the symptom, plus a brief description and then HOW TO TREAT IT.
You'll see an emphasis on improving water quality but you're not left wondering how to do that. Everything is spelled out from lighting to filtration, medications and resources on how to use them –
The site focuses on Amazon.com-availability because they have Prime shipping, which allows virtually overnight delivery of most things.
You're just LUCKIER when your local pond supplies store has everything in stock.
Many times they do.