Why I can't put all of my trackers in the file that is being downloaded.

For example
I'm downloading a file, and I will add all of my trackers' list, that's being saved in my computer, to the file that being downloading. All of them were paste then I click "OK" then when I view again all the trackers, I only see 78 only but I put 150++ trackers. What should I do, I have slow internet so I need those trackers.

there might be a limit to how many can be pasted at one time. try adding the trackers in sections (like about 50 at a time).

or in the settings->transfers->trackers you can add your list to the 'Add these tracker URLs:' and then when you start a new torrent all those trackers will be added to the torrent. Trackers put in here will ONLY be added to NEW transfers, not to transfers already in tixati.

You have it backwards. If you have a slow connection you want to use the lowest number of trackers you can. You are wasting your bandwidth speaking to trackers instead of peers. If you add trackers but no one else has added that tracker for that torrent you will not get peers returned from it. So any communication with that tracker is a waste of bandwidth. Besides that you are putting a useless load on the tracker that it does not need. This hurts the whole community.

You would be better to delete all the trackers that don't show higher numbers of seeds and peers. The seeds and peers from those trackers will lead you to others by using pex and DHT.