sick?

I think I've done harm to my largest avocado. I went to change the water, dumped the whole thing out and refilled fresh. But either I bumped the taproot in the process, or it sat too long between water changes, because half the root has become brown, and it looks like mold is growing. Dismay. The stem doesn't seem to have grown any since, either. I feel bad to have this one fail, as it grew so well from the start. But if it does, there's four more steadily coming along, and I'll know better how to treat them...

Funny, there are little bumps all along the taproot, which I thought at first would become more roots. But they did nothing, more roots have grown out of the base instead. Is it sick? or are those bumps not supposed to become roots?