Well done with the Prazi. Nice about the babies in the pond as well! So that is a good question about treating new fish if you ever get them! I would definitely quarantine them for about a week to make sure they are not sick. THey could have a variety of diseases that you would not want to introduce into the pond. But I would not treat them unless there are signs of something wrong. Remember the parasites you probably had were introduced by birds (almost certainly) and not fish. That could happen again. As a general rule dont treat for something that is not a problem until you know there is a problem. You handled this recent problem very well and you are looking after your fish responsibly!!