Consider that it might not be the problem of the detritus settling on or in the rocks. You could blow it off but that just puts the junk back in the water column. I think small amounts of that type of biological filtration, the LR, are very important and neccesary for what you are trying to achieve.
I would also consider the possibility that you may have gone a touch to high/fast with your bioload and your feedings. I understand your mindset with indirect and natural feeding of your sps, however I'm starting to think that this can be achieved with a much more subtle bioload.
Or, look at it this way, if you had the bioload with a larger sump it might not have been an issue.
All things being equal- and it sounding like you have a firm grasp on all your other parameters, I would say you have two options.
1. Lower the load
2. Increase the water volume