there is nothing wrong with fw dips. i do them to fish at the pet store all the time. along with sw dips on the fresh fish. uselly about 5 mins too. never lost one. but i have gotten a heel of a lot of parasites pulled off of fish that way (mostly flukes). fresh water dips are not going to kill a healthy fish, and if he has parasites hell be glad you did it in the end. you wont be able to see them all. most parasites dont let you know they are there. i do it to angels mostly but ya if he has one you can bet on some more.