Recently one of my guppies had babies and only 2 survived. I got another 6 from a friends "litter." The other day I looked in the net and one of the babies was dead. I thought this odd. And then the next day, another one was laying at the bottom of the net. I thought it was dead but when i fished it out I realized it was alive. I put it in a smaller bowl and looked at it. It was fine except it couldn't swim right side up. So far all the rest look healthy and are much bigger than the others with problems. Any ideas to what was wrong with them and how to prevent it?