Snapping hair, bleaching roots

Hiya,

So I've been going to blonde after being blue and purple for a year.

The purple was murder to get out and now, as I realise using crazy colour back to base twice was a mistake. My hair began snapping off. Fortunately I have thick hair so it's not been too noticable except for the little shorter hairs at the top of my head.

Just yesterday I  used a protein hair mask which has restored the overall feel of my hair. Which I'm so relieved about.
Though I'm still apprehensive.

I'm at the five weeks mark for my roots. I certainly do not want banding, as I want to tone my hair white. I'd have done it at the four week mark if my hair hadn't taken this turn. I'm thinking maybe next week but I'm still fearful.

I always coat the rest of my hair with coconut oil while doing my roots but I'm aware run off does still happen and affect the rest of the hair.

I dont want to make a bad situation worse. Although,  I'm thinking maybe coating my hair with coconut oil and some more hair protein.

I'd really not like to leave my roots untouched as my natural hair is very dark so banding is a real problem for me. Though I have a feeling I should...

Any advice? Thanks in advance.