Gyre pump out, propeller in

We are removing an IceCap gyre and installing an AI Nero5. The gyre worked well, but was hard to clean and to obtrusive in the display tank.Our design approach is a minimalist glass box.

Very little return flow

The return flow from the sump was just a trickle. Tried different pump speeds but no change. Did the return tube plug? It looked OK. The braided nylon tubing is about an inch wide, clear, and some algae at a…