Fiber optics cable & connectors

I am installing a fiber optics link to extend my network about 400m from the main office. My problem is that my fiber cable is 300 series while the accessories like the 2SC connectors are for 900 Micron buffered fiber. When i make a small patch cord, it works, but when i try the 400m stretch, i dont get any link. Please educate me if i am using the wrong combinations like if i have to get a 900 series cable before my connectioncan work.