Yeah, reduce the flow, from pics it seems the fluidusing action is a bit on the turbulent side.
This will result in too much abrasion of the balls, consequently having micro particles in your tank.
There were some studies a few years back where phosguard showed to have a negative effect on especially soft corals. Even though multitudes of the recommended amount was used in the studies, mirco particulate aluminium oxide should be avoided.
The action should hardly move the beads, just a light action.