thanks for the replies. This is an outdoor system with about 500 gallons of water at 55 deg F. I wouldn't be able to heat it to 85. The temp was down to 47 several days ago, but our nights haven't been as cold lately.

I read on wiki that the parasite can only survive about 2 days without a host. I'd rather not try to remove the goldfish for a few days. I'll add some salt and keep an eye on them. They don't appear stressed - just noticed the white spots on a few.