anyone aware which tracker[s] does ru.tk api uses?

To successfully use popcorn now a days, the API to use is ru.tk. I prefer to use rtorrent for torrents purposes, and I uesd to believe yts was the tracker popcorn uses, however I've found stuff on popcorn, using the ru.tk api, which can't be found on yts. I'm wondering what tracker[s] does that api use to grab torrents/magnets from, so I can, if I prefer to, go search through them, if they have webUIs that is...