I had the same problem. Your flow is too strong. I went through 3 different pumps and landed on the following. It is the smallest pump I ever seen but it works.
Jebao/Jecod DCS-1200 DC Water Pump 320GPH 4.9ft for Marine Reef Tanks Sump Skimmer Protein
https://a.co/d/j0SH3B3
Also, is your discharge pipe fully submerged? If so then angle it so the pipe pours out into the water. If submerged I found it creates a siphon.
Also, you need strong air flow to tumble the media. If it's still not tumbling then I would look at upgrading the air pump. This is the pump I have.
EcoPlus ECOair 5 Commercial Grade Air Pump 1300 GPH - 80 Watt Single Outlet with 8 Valve Manifold
https://a.co/d/ceIHevt