I had an issue of low flow through my sump as well. It did cause a bigger problem in my tank. With about 2x turnover through my sump, very little nutrients were being moved to the sump for removal via the skimmer and macro algae. The result was a slow increase in algae in the DT. Actually, not really slow, because once it started, it built up kinda fast. I have since replaced my sump pump with a DC
pump giving about 900-1000gph flow and around 8x turnover. My algae problem is slowly going away and my skimmer and chaeto are both exporting much more.
Point is, be careful with too low of sump flow.