Hi there
I have one monetizing page, and 20 IG acoounts. Can I add link to my page to all accounts?
I was warming them in last 3 weeks - 20-50 follow a day with some random rests.
Or should I use some link shortener services?
You will get banned. Spent more time for read all topic here. Many great topic already posted.
If you add the same link to all accounts there is a very high probabilty of getting them all banned. Search the forum as @guntoroid there are very good discussions on how to do this and also ideally search the forum before creating new topics of stuff that’s been already discussed a lot 
I’m making 500+ followings after first week ( which was increased gradually by 50 followings each day ) and i thought i was making a safe warming until I read your post 
20-50 for 3 weeks ? damn