I've got a Felt X-City with the Shimano Nexus 8-speed internal hub, so I need to adjust the chain tension through the bottom bracket. It seemed easy but I am having a problem, so maybe I'm missing a step. Here's what I'm doing:
1) loosen the 2 hold-down bolts at the front of the bracket (shown by the arrows in picture 1)
2) use a spanner to turn the bracket until chain tension is at desired level (using the 2 holes indicated in photo 2).

But the spanner tool, which fits great, won't budge. Should it be that hard? Or do I need to use 2 spanner tools at the same time, one on each side?

The LBS adjusted it before, so I know it can be done!