You'll have to explain a "fuzzy" image. It doesn't take much bandwidth to stream HD from YouTube, probably 5 Mbps, 15 if UHD.
Stats for Nerds is a good start. If you have a Roku remote, Down Arrow...you'll see the Progress Bar...Up Arrow to the round icons...Stats would be the last icon. The Roku OS also allows you to check your connection: Settings > Network > About > Internet Download Speed. Of course, this only reports what your connect is capable.
by fuzzy, I mean the picture is out of focus most of the time, as in watching golf, the players look out of focus, then the pic clears momentarily, then out of focus again, and is that way most of the time. it's like trying to see the golf ball without glasses on if you have poor eyesight.