I understand the corexy belts. It is similar to your delta where multiple steppers move together to generate motion on one axis. On the delta it is a blend of all 3 but on corexy it is just x and y that blend. The color coded diagram of the two belts on top shows how this motion will work..

I know those belts need to be tight. But even more important I know this printer just like the Tevo Black Widow is a problem child right out of the gate. The reviews I saw from early 2017 on the BW that called it dangerous and a fire hazard and other terrible names is what got me all excited about getting it. And why I never put it together the right way from new. And that is exactly what this is because that is what is exciting to me. These are the tronxy x5sa pro reviews that helped push me to it: https://www.youtube.com/watch?v=KiJg7f9ib4M&t= . And also https://www.youtube.com/watch?v=cosb_F8NRIM . Now these are people reviewing the machine exactly as it comes and have made absolutely no attempt at correcting anything at the time of these reviews. I will draw up and print out some new motor mounts and for the X gantry I will make some pieces to attach to each end and keep the gantry square. Until I get HIWIN rails and guides and a 1 piece gantry going. But I am aware of it's shortcomings and can't wait to tackle them. As I understand it the biggest problem I need to overcome is the top 3 piece assembly that make up the gantry and how it does not want to stay square. Here is a picture of it all together from their website..