If this is for a reel where you are using 200 yards of backing, chances are you are not trout fishing. I think the blood knot would be fine for trout fishing where you are not stressing the backing near the breaking strength. But, if you are going after larger fish that may pull close to the breaking strength of your backing, I would recommend that you use a stronger connection.

The best connection, if your backing braid is hollow, is to splice the two spools together. This is not hard to do, if you have one of those Cortland tools, and will make a 100% connection. It is slimmer than any knot.

If your backing is not hollow, tie a bimini twist loop in the end of each spool of backing and loop-to-loop those together. This is also a 100% connection and pretty slim as well.

Regards,
Ted