Towels spa and rehab day!

Hello, I am planning my towels' spa day this weekend! My biz powder is arriving tomorrow!! I have a couple of questions

• can you confirm that biz alone should be used in the tub soak?
• when the time comes for rehab is it ok for the ammonia to touch the biz that is on my wet towels?
• I am buying my ammonia at Canadian Tire but it's not indicating the percentage. It's folded lemon sudsy. Does it matter?

Thanks. I am so exited about laundry! Thank you for the great write up kismaiaesthetics!!