There is only one fool proof safe manner to feed your fish feeders, and that is by raising your own feeders under controlled conditions.
There's no option B, everything else involves risks.
FYI - while salt and high temps can help control ich (sometimes) it does not make a feeder fish pathogen/bacteria free. Not even close.
And Daniel was correct in stating that it takes stress to trigger a health issue, but unfortunately you have now introduced possibly 1 or more pathogens into your system that may live there until one of your fish does come under some form of stress, and then guess what happens next. 1 week with no issues doesn't mean that you dodged a bullet, it could mean that you simply dodged a bullet for now.