so i started using the rapid rooter system and am pleased with it. however i have found that some of my clones have brittle stalks.

i have only found a few like this.
i did the transplant. everything was growing fine. bout a week after transplant i bumped a clone lightly and it snapped. there was no fiborus quality to it what so ever.
i checked the other 15 and 3 more of them had the same problem.
the rest were right as rain.
if anyone could explain this it would be much appreciated.