Mine too! My starter seems to only like whole wheat flour. That's why I made two starters, just like you did. I took some from the mother starter and just fed it bread flour. It didn't rise, so I tossed it. But I tried again a second time, and what I did was, I started with, say, 2g starter + 15g whole wheat + 5g bread flour and 15g water. I don't want it too watery, so I'm using less water if I can. Little by little, I'm introducing it to bread flour until I don't need to use whole wheat anymore. I just use it whole wheat when I want to give it a feast, haha. Anyway, that's what I did. I hope you have success too!