How does he
KNOW this? See, what you [not
YOU, but people in general] have to understand is the "cause and effect" mentality. There are so many factors that go into having a healthy pond, and everyone does things different. We tend to do what works for us, in our situation. And no 2 ponds are alike. So who can really say what the magic, secret ingredient is.....? Personally, I'm a fan of science -- show me studies that prove/disprove, or give me a good, scientific-based rationale . I never add salt and as far as I know, I don't have parasite problems. Yes, salt will stimulate the slime coat, but again, there should be enough "salt" in the source water [from the tap or well] to fill any needs the fish would have. If someone's water was in question, they can always have it tested for those elements.
And some people do add salt and swear by it....and they never have a problem.
In the end, you have to make that decision on your own, based on whatever "evidence" works for you [again, using the generic "you"].
The absolute best thing anyone can do for their pond is to keep it clean and maintain the best water quality possible [and always quarantine new fish!]. That's the real secret to parasite-free fish.
As to the "parasite" issue, again, think "over use of antibiotics." Let's say your fish are constantly being bathed in brine [like the "experts" recommend]. Then a problem pops up that a "salt dip" or "salt bath" would normally take care of. But, those darn little parasites that are bothering your fish are now resistent to a very simple, harmless, and inexpensive method of treatment. Which means you have to try other things.....treatments that might NOT be simple, harmless, or inexpensive. Just saying.......
And back to the "cause and effect" mentality....... Here's a story I've always liked. Grandma passes down her recipe for the most delicious post roast ever..... Grandma got it from Great-Granny, etc. So the daughters have followed the recipe religiously over the years. Step one says to cut the ends off the roast. Always been done.....never questioned.....delicious roast.....gotta do what the recipe says. One holiday all the family is together for a meal and Grandma decides to help in the kitchen. She see's Granddaughter chopping off that beautiful meat, so she asks what gives? Grandaughter says, "Well, Granny, that's what we've always done so it must be the 'secret ingredient'." Then Granny starts to laugh and tells G-daughter that the reason Great-Granny cut off the ends of the roast? Her pan wasn't big enough to hold a whole roast.......
The cooked roast was so good.....no one ever questioned the rationale......therefore, cutting off the ends of the meat is what made the roast taste so good.
Hmm, now I'm hungry!