I looked at the runt tank today and realized that I was missing some of my juveniles. Couldn't figure it out until I checked the filter well....sniff... saved about 5 but lost about 6 others. Most of the females....didn't have many to start with.
Sorry to hear that.
If they are getting stuck to the filter, then its too strong. I would suggest getting a sponge filter or wrap a nylon stocking around the intake tube so they can't get sucked up.
It was only in there on a temp basis to get some bacteria into the bio wheel. I thought they were big enough to avoid that. Lesson learned the hard way.