I only have a small sump system running five sub 15l tanks, I started off with a Resun King2, but it died after about a year. I stripped it down, but could not see anything that would impede the flow, such as the usual snails :evil:
Because I did not have a spare at the time and none of the LFS stock Laguna or Eheim I had to buy another pond pump - cannot remember the name - it is starting to get rattly and annoying.
I have a second hand Eheim that I am tempted to put replace it with, but the flow rate may be a bit too much for my little tanks.