I have the same issue with both my 4K Gyre. I'm giving it a ton of force and can't get it to budge. I emailed Coral Vue support and this is the answer I received:
"You should not have to remove the impeller shaft during normal cleaning, only when replacing the shaft or the motor block...
Here is what I use for my fan in the summertime:
If Tmp > 78.5 Then ON
If Tmp < 78.0 Then OFF
If Tmp < 70.0 Then OFF
In the winter, I plug in my heater to the outlet where my fan was plugged in and adjust the programming to:
If Tmp > 78.5 Then OFF
If Tmp < 78.0 Then...
I purchased this one 4-5 months ago after watching a youtube video by Melev. Works well, just be sure to purchase some additional batteries. https://www.ebay.com/sch/sis.html?_nkw=High+Power+445nm+Focusing+Blue+Beam+Laser+Pointer+Pen+Burn+Match+5MW&_id=332250403980&&_trksid=p2057872.m2749.l2658
I've used a 317 GPH Quiet One for years. Finally had one go bad after 5-6 years and spent another $20.00 to replace it. It mixes all my salt water in my Brute, then I attached a 25' hose and fill my tank after a water change.